I’ve heard lots of wonderful stories about Keanu Reeves, including giving around $80 million of his income from the Matrix films to the crew (edit: cite). And I just saw a .gif of him being discreetly filmed riding the subway and offering his seat to a woman carrying a big bag, so there’s that, too. I bet he even helps old ladies cross the street. 
Adam Sandler is one of the greatest actors in this generation of actors. He has been in such blockbusters as The Waterboy, Little Nicky and Jack and Jill.
The Waterboy is basically Hamlet on a football field.
Please tell me this is a whoosh.
Johnny Depp once visited Great Ormand Street Hospital dressed as Captain Jack Sparrow and read stories to child patients. He also donated one million pounds to them the following year. It was to thank them for caring for his daughter during a serious E. coli infection. Seems like a pretty nice thing to do. (cite)
Which is why, on the rare occasions I’ve run into celebrities in public places, I leave them alone and pretend I don’t recognize them.
I have met and spoken to a few minor celebrities, but in every case it was because a mutual friend introduced me; they were perfectly nice, but arguably being civil to fans is part of the job description. No way in hell would I accost a celebrity who is trying to eat lunch or buy a quart of milk or whatever.