The first thing that comes to mind that I would do it to tell them to grow up
It is immature of them all, and maybe they don't know what mature even is. I know it might be tough if you are timid and can't really stand up for yourself, but that just makes it that much more effective once you do.
Tell them the joke got old three and a half years ago. You don't need to take what they are feeding you, to get you mad about it, because that is what they want to do. I'm a more aggressive person by nature, so I unfortunately might not relate to you, but do you think you could do this, stand up?
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