A man walks into a bar. Millions do so on a daily basis. So the crossover of that theme is inevitable. But the twist you put on that as a writer or comedian is uniquely your own. It's the product of countless hours of creative torment and basically your bread and butter.
So I certainly struggle to accept the notion that imitation is the sincerest form of flattery. Try selling that ideal to the fraud squad.
A great gag, like a homing pigeon with multiple personality disorders, will, once released into the public consciousness, return to you one day in some vaguely recognisable form. But that's inevitable and the price of going public with your thoughts. The audience pay for the privilege of sharing what they've heard with the uninitiated. A fellow comic "sharing" your ideas with an audience is theft, pure and simple.
Unfortunately, within stand-up, plagiarism comes down to a question of morals. Remembering the exact moment of conception, subsequent tweaking and initial telling of a gag is easy. Proving yourself to be the intellectual owner of that same thought when, if executed properly, it is presented merely as casual perception? That's practically impossible.
The saddest thing is though; little is ever said to the perpetrators themselves. Their shameless audacity often leaves its victims dumbstruck, almost fearful to protest. I myself have sat in dressing rooms, feeling like a pensioner asked to point out a mugger from a police line-up, but without the security of a one-way mirror (although I'd best point out first, before every other comic does, that the contents of my comedic purse were wholly sentimental and worth nothing of any real critical value).
I can never help nodding in admiration as Matt Damon's character in Good Will Hunting explains how he would rather be serving fries in McDonald's than be unoriginal. I could've taken that sentiment and presented it as my own but, despite what you might think of me, I'm really not that big a twat.