I think the number of people who turn up to chess clubs so they can flip over the table part-way through a game is pretty small.
If RPGIng has a significantly larger number of such participants, that would be a worry. But I don't see anything in the OP to suggest that that is what is happening here.
If A is bored by B's play, and therefore takes steps to make things interesting, without knowing more I have to treat it as an open question whether it's the proactive A or the boring B who is "in the wrong". But in any event that's not what I saw in the OP: a player, presuably playing his PC is frustrated by the Mad Tyrant and verbalises that frustration, then the GM narrates more stuff which includes an escalation to violence, and then another player has his PC respond in kind:
{A PC] yell[ed] out something to the effect of "you're crazy and don't deserve leadership here." For this affront, the ruler yelled for his guards to come and arrest that character. In response, another party member tried (and failed) to grapple the ruler and put a knife to his throat
That's the GM, not any player, who treated violence as the universal solvent.
Nice job with the partial quotation, there.
The party got a private audience with the ruler and things were moving friendly enough, when a player (probably bored with the negotiations and playing the "but I have a low Charisma card") decided to trump the party's hand and yell out something to the effect of "you're crazy and don't deserve leadership here."
Do you see where the OP says the player is "probably bored"? (This is a player the OP says later is behaving similarly in another campaign, so ... probably not the character.)
As to who instigated the violence:
For this affront, the ruler yelled for his guards to come and arrest that character. In response, another party member tried (and failed) to grapple the ruler and put a knife to his throat to take him as a hostage.
The Mad Tyrant is behaving in character; it's a second PC who instigates the violence.
First, as with @chaochou I'm curious about what the resolution method is that was used to make the move from PC yells out to Mad Tyrant takes it badly to Mad Tyrant calls for guards to guards arrive and follow his order to arrest PC. At every point I can see a different possibility: the Mad Tyrant laughs off the insult; the Mad Tyrant personally challenges the affronting PC to a duel of honour; the guards are all drunk and don't come when called; the guard captain agrees with the PC that the Mad Tyrant doesn't deserve to rule, and seeing now a chance to strike against the tyrant takes up that chance. And I came up with those possibilities in the time it took me to type them up.
And none of those may be in character for the Mad Tyrant--who was described as not tolerating dissent. Certainly "laughing it off" is pretty much the opposite of that. And drunk guards? Might as well have a divine figure on a ladder come own to interrupt the execution.
Second, the Mad Tyrant isn't a natural phenomenon. It's an element of the fiction in a RPG, presumably intended to serve some purpose for RPGing. What's that purpose? To create a puzzle for the players, where if they don't guess the right thing their PCs die? (This is @Nagol's analogy to the trapped door.) To allow the GM to tell the players what their PCs should do on pain of dying? A chance for the players to show off their ability to follow the GM's lead? Something else?
The party sought out this audience. It doesn't sound from the OP's description of play that the plan going in was to try to assassinate the Mad Tyrant. This isn't "I failed a check and the trap blew up in my face." This isn't "I couldn't figure out the puzzle the GM put before me." This is "I pissed on an electric light socket."