Can you try to work out a system with them?

Where if you say "We need to stop this conversation/topic/teasing" that they'll actually respect it and stop? Explain to them that sometimes you might be able to handle it, but that when you can't, that you don't want to snap at them when they don't really deserve it, and you need their help by respecting your wish to end that topic.

I tend to just go "NEW TOPIC!!!" if something bothers me and I notice it's starting to trigger me. Most people are quite respectful of that. I just say those two words, or something "We need to stop talking about this" or "Can you change the topic? Now please?". If someone DOESN'T respect that, I'll say it again and usually explain that it's starting to upset me or piss me off.