Paul Rudd is, of course, immortal. Here he is in Clueless in 1995:
And here he is now:
Basically the same after 21 years. Naturally, someone who is immortal is more patient than the average person, which is why Rudd has been playing the same gag on Conan O'Brien for the past 11 years. It all started during the promotional tour for The 40 Year Old Virgin in 2005. Asked to furnish a clip for O'Brien's talk show, Rudd obliged. However, it wasn't from The 40 Year Old Virgin - it was from Mac and Me.
In case you don't know, Mac and Me is possibly the worst movie in history. A rip off of ET, it sees an alien come to Earth and help a disabled boy, which in itself would be egregious enough as a plot, but with profit-sharing and product-placement deals in place, let's just say a lot of help also comes from eating burgers and even from Ronald McDonald himself.
Rudd wasn't actually in Mac and Me, so what he provided was perhaps the worst scene in an already terrible movie.
And since then, every time Rudd has appeared on any of Conan O'Brien's shows to promote any of his new movies or even plays, he's provided exactly the same clip for O'Brien.
Actually, that's not quite true. Although O'Brien quickly rumbled what was going on and soon was in on the gag, movie studios started trying to get Rudd to provide genuine clips. But that doesn't mean the immortal Rudd need do as they say. Not exactly, anyway.
PS Rudd's Captain America: Civil War co-star Chris Evans didn't know about this. Here's Rudd explaining it all to him (after this interview)