When someone laughs at my jokes they instantly become more attractive.

It's not the only thing needed to make someone hot - I don't think I know of one thing that would do the trick regardless of anything else... but it's a big leap towards it for anyone, because it combines them laughing and having fun (which is attractive) with making me feel appreciated and included and good about myself (which opens me up socially to feel attraction).

On the flip side, someone who doesn't laugh at my jokes will become irrevocably unattractive regardless of anything else.