Re unfunny jokes: I have a co-worker who likes to send out "funny" e-mails on Friday afternoons. Once, he was laughing his head off at his desk, and when I asked what had tickled his funnybone, he said "Oh, didn't I copy you on this e-mail I wrote? Here you go!" He then practically stood over me while I read it, looking at me expectantly. I managed a few sincere-sounding "Ha ha"'s, but boy oh boy, he's not NEARLY as funny as he thinks he is.
Re people not taking advice: a while back a friend of mine was worried because her bosses had asked to meet with her the following day. She wasn't happy at her job, and she knew that she wasn't doing very well at it, so she was concerned that she was about to be fired. She said to me "I'm probably worrying about nothing, right? I'm sure they're not planning to fire me." I asked her to tell me exactly what they'd said, and when she was done, I said "I'm really sorry to say this, but I think your first instinct was correct. Better start looking for another job, just in case." Well. She was REALLY mad at me, saying "You don't know that!" "No, I don't, but you asked for my opinion, and that's what I think." "You still don't know that! It could be nothing!" "Maybe. But maybe not." Sure enough, she was fired.