Unbeknownst to an unarmored character and despite the DM's sufficient telegraphing, they touched a chest that has been smeared with a dangerous contact poison. The DM describes the greasy feel of the poison and asks for a Constitution saving throw.
"Wait just a minute!" exclaims the player. "I imagine my character is wearing gloves. They have traveler's clothes on."
The DM considers this. There is nothing in the rules that says any clothing set comes with gloves, nor any armor for that matter except scale mail, chain mail, or plate which come with gauntlets at least (none of which the PC is wearing). There are no gloves in the equipment section to purchase, and the character has no magical gloves.
Is it reasonable that the player believed the clothing set they have comes with gloves that they are wearing even though it's not specifically listed on their character sheet? Does the timing of establishing this fact - after touching contact poison - matter to resolving this issue? Do you as DM side with the player's seemingly good faith belief that the character is wearing gloves or are they making that saving throw?
In short, how does this get resolved at your table?
I mean, what you
don't do is tell the player that their PC is
not wearing gloves.
Gloves are a basic medieval essential. They're some wacky modern invention. They're not something barely anyone owns. That the equipment list is missing them, and the outfits don't describe them is a hard strike
against 5E, not against
the player. None of them describe hats, either, but the idea that everyone is walking around bare-headed is absolutely laughable! The closest you can get to owning a hat in 5E, if you follow the descriptions, is you can have a cloak with a hood. It's obviously down to 5E's terrible equipment section.
A lot of the DM suggestions here are basically of the:
"I get out of bed"
"GOTCHA! Take 1d6 damage!"
"What why?"
"You didn't say you took off the blankets first, so you got tangled up in them, fell over and hurt yourself!"
DMs who would tell a PC they weren't wearing gloves are basically "GOTCHA!!!" DMs. If you asked the player beforehand what they were wearing, and got into to specifics, and there were no gloves, sure, but they'd know that too, and they wouldn't argue.
Players often have very specific visions of what their character is doing that is not necessarily expressed, and just trying to overrule that for the sake of a "GOTCHA!!!" is... well it's not good DMing. These visions are often informed by fiction. In fiction, thieves/rogues/etc. are typically portrayed as wearing gloves. Why? Because it makes sense that they would be. If they're doing stuff like climbing, handling sharp weapons, maybe poisons, being out in the night (which is usually cold) and so on, they'd want gloves.
Similarly the idea that the PC is poisoned, and they have to work out why is ludicrous, and defies the basic approach to fiction that 5E has. It would absolutely fine in a lot of RPGs, which operate in a much more abstract mode, and where players are expected to operate that way? But for D&D, silly at best.
The best answer was given almost immediately - the outer layer of the gloves are now poisoned - and that's going to have consequences down the line.