I am going to talk it over with my DM for sure, but first I wanted some input from you guys here. So far I get feedback that my PC and his reputation are inconsequential and do not matter and other PCs can stamp over months of effort as they please.
No, you haven't gotten that feedback. You've gotten the feedback that premeditated poisoning of someone for a non-violent act is evil, and that intra-party killing breaks games, breaks friendships, and ruins fun. You haven't liked that feedback, but that's been the majority opinion.
The thing about PC death is that it's permanent (especially at level 5!) Reputations are salvageable, fortunes come and go, but a dead PC is gone for good. Before you need to decide what to do, you need to answer yourself a couple of questions.
Is it going to ruin your fun, out of character, if the rogue goes ahead? Is it going to ruin the rogue player's fun if your PC murders the rogue after the rogue goes ahead? If either or both of these go ahead, what effect will it have on the campaign, the gaming group, or the friendships within it?
Real life friendships trump in-character stuff, always. Games aren't worth losing friends over. Playing faithfully in-character is not worth ruining other people's fun. We're not method actors.
If, however, the real-life people (including you) in your group are 100% ok with this vendetta escalating and can laugh about the PC oneupmanship and over-the-top in-character conflict, then you certainly do have options for getting back at the rogue PC nonlethally. Even if they have no reputation, no friends and family etc. Your PC in the rogue's body at the moment, right? Presumably, at some point you'll revert back. Perhaps a huge embarrassing facial tattoo might be in order, in the meantime? Or borrowing a huge amount of money in their name, and then skipping out on the loan. You've got money - bribe all the other PCs to steal all the rogue's stuff while the rogue is asleep, dump him/her in the worst part of town naked and weaponless and painted purple, and then leave the city. There's ways to recover your reputation too - find a random corpse who somewhat resembles you, dress it up in the rogue's silly outfit, then cut off all its appendages, tie it to a stake and set fire to it in the town square, as public as you can. "This is what happens when people cross me"
And you mentioned the PC who is evil should be out. Well, is my wizard really the evil character here? Or did she start the pvp? True, she did not steal from me, or hurt me directly. But the loss of face and business opportunity will amount to huge loses of gold. And huge amounts of wasted time and resources put into building it. Who is really the bad guy here? The way I see it, there are two somewhat bad guys at a clash, but it is not my wizard who started it and should not be to blame.
You can't simply absolve yourself or your PC of blame here by saying 'they started it'. As you say, there are two bad guys, the rogue PC sounds like they're acting like a complete jerk, but you're the one who's hugely escalating the situation to the point of intraparty killing - especially when the rogue, to some, might just appear to be pranking. And given what you've said about the NPC wizard in your original post, it sounds like your PC makes a habit of wildly over-the-top and out of proportion retaliation. Is it in character? Maybe. Does it matter if it's in character? Probably not very much. And even if it is in character, it's only in-character because you chose for it to be when you made that character. Maniacal vengefulness is a very double-edged PC personality trait. Reputation is only hyper-important to your character because you made it so. These are not matters that are outside your control.
Special pleading about medieval moral standards and the historic value of reputation etc doesn't cut any ice with me, frankly. We're not medieval, and D&D isn't medieval in any recognisably historic way other than 'swords are a thing!' And also, consider whether you'd accept this from another party member? You say the rogue is a brutal thug and your PC is wealthy - how would you react if the rogue asked you for a huge amount of your cash for a new magic item or something, you said no, then the rogue decided to cave in your wizard's skull in the middle of the night because 'my PC is a brutal thug and the wizard has lots of gold, it only makes sense for the character that i'd kill him and steal it, and he started it by being tight-fisted!' Because there's not a lot of difference. You came here asking for input, and you're getting it, even if it's unwelcome. I understand where you're coming from, and I understand the situation isn't entirely of your own making, but that's how it is.
In the end, i'm not your DM and I'm not the boss of you, I'm just telling you how I'd adjudicate something like this in my game - but as a DM, I'd 100% warn all parties involved ahead of time in very clear language. And if they both persisted, to be honest I'd probably start looking for another group because that's not the sort of thing that I personally enjoy in my games. If you're playing in a game, or under a DM, where lethal PVP is considered fun or intraparty murder is not considered evil or jerkish, then that's a very very distinct rarity. If you go ahead, be warned that it may well get you kicked out of the group, and pleading medieval justice standards is unlikely to help your cause.
Is the rogue also being a jerk? Hell yes. If they're doing this for some sort of out-of-character reason to get a rise out of you the player, especially with the juvenile cross-dressing stuff, then they're being a HUGE jerk and as a DM i'd be telling them so. Is there any reason why the rogue and wizard would adventure together after that? Hell no, and that's a mess both players and the DM will have to sort out, which is why i encourage you to have this conversation before things become irreversible. DMs in my experience HATE having carefully-planned campaigns derailed by this sort of thing. But killing a fellow PC is the nuclear weapon of D&D. Even if they started it. No matter the provocation. Be aware that it'll likely be treated as such.
This is why
@Lanefan asked you about the group dynamics I think. How well do you know the other players? Do you play with a group of long-time friends who socialise outside D&D? Have the other group members been playing together for a long time and you only joined recently? Are you a group of strangers who met recently on the internet and started a game? Every group has an implied social contract, standards, lines that are not stepped over etc, and they all vary from group to group. If you're new to a group, you may not know those standards, or perhaps a brand new group has never really talked about this stuff or settled on standards at all. Maybe you're in a game with people who do PVP stuff or nasty pranks or gaybaiting/gender based humiliation all the time. Frankly, all this should have been sorted out at a session zero before the game even got started, but that's water under the bridge now.
In most high-functioning groups I've been in, the solution to this sort of thing is that both players bend a bit, out of character. Here's some advice -
don't be the one who refuses to bend. Genuinely offer a compromise that gives the rogue's player part of what they want, and do it in conjunction with the GM. Be aware it'll mean that you won't get all you want. D&D is a cooperative game. If you're at each others throats in or especially out of character, it won't work for very long. They may absolutely refuse to compromise, but at least you tried, and that'll maybe give you a tiny bit of moral highground for dealing with what comes next.
