Some good points, but let me clarify a couple of things. It was on one bead, removed from the necklace that was eaten. It isn't My Guy syndrome. That would require some degree of character consistency. The character's personality changes at the drop of a hat, the only common thread being extreme egotism. He is playing CN and so far his antics have only caused IC issues, not OOC issues.

@Overthinks Ah, I misread your question, but it doesn't change the interpretation of rules. I'll edit for clarity.

@Overthinks The majority of cases where I've seem MGS invoked have been Chaotic Neutrals "just roleplaying their alignment". I may be jumping to conclusions, but I detected a hint of annoyance in your question, and responded based on that - I'm sorry if I misinterpreted your question.

you're not wrong about the annoyance. But when you players are having fun with it, sometimes a GM just has to think fast and roll with it.

@Overthinks Sure thing - but don't forget that your enjoyment is also important, and that the other players (including the player of the Tiefling) might dislike the zany behavior too, but feel obliged to not protest against it. :)

@kvirri, the character playing the Trifling's mature older brother usually beats me to it. At the start of the campaign I made sure everyone had at least one close personal connection to another PC. (every loon has a close connection to "straight man". I am sooo happy I did that. )

@Overthinks If you'd like, pop in Role-playing Games Chat to share your experiences :)

An additional point against simply killing them, from what I've seen happen: repeatedly killing irritating characters means that the player will learn to not get attached to their character, which means they're often more likely to do dumb things, because they don't care about the consequences, because they're not invested in the character at all.

I am not sure how likely this is to be my guy syndrome (they're just doing something for fun), but I agree with the rest of this advice.

I'm not sure about the not killing part, and considering the OP's comments, this is definitely not MGS. I've seen this kind of behavior multiple times, and it usually is the result of the player not caring an inch about his character. He just does random stuff to have fun, and doesn't actually consider what his character would or wouldn't do, or what should be done in certain situations. Killing his character so he can create one that he likes and can roleplay coherently might even do him a favor.

@BgrWorker No, asking the player whether that is the case and trying to remedy the problem would be doing them a favor. Killing the character without so much as a discussion would set a really nasty precedent.

Would this really be killing the character on a whim? If a character swallows live explosives to see what will happen, having him explode seems like a quite reasonable consequence consistent with the (rather stupid) decision he made. Personally, I think that having it not explode immediately is preferable, mainly because "You now have unexploded ordinance in your stomach" is a much more interesting scenario than "Nothing happens" or "You die". But if it does kill him, that's a result of his choice, not the DM's whim.

@Ray Whether they are live explosives or not is a GM's choice. Whether the character's fire resistance indeed protects the character (as the player seems to believe) is the GM's choice. Whether the character dies or not is the GM's choice. Qualifies as "on a whim" in my books.

Wait, fifth edition removed the bit where the beads explode when hit by fire damage? That's the best bit!

so it explodes when hurled ? Do not induce vomiting.

"What should happen (rules)? In my opinion, nothing." Either you're talking rules, or you're talking opinion. Why is there a mention of the rules above a paragraph with opinion and without rules?

@Mast Rules written in natural languages are often ambiguous and up to a certain amount of interpretation. The rules regarding the necklace state that a bead has to be hurled using an action to trigger the explosion - that part is not my opinion. My opinion is that the bead going through the tiefling does not constitute hurling it.

@kviiri Ah, that distinction wasn't clear from the text as written.

@DanHenderson I agree, and that's a major reason why I'm not a huge fan of DnD. However, offing a character for a single humorous and not foreseeably obviously deadly action is still on the more whimsical end of the whimsy scale.

@kviiri I'm just not there with you the "not foreseeable" nature of the act.

@DanHenderson Fine, don't. I've already made my stance perfectly clear in the comments and the post.