My kittens do this daily. They take their small little heads and poke it in my cup. I'm pretty sure they think the cups of whatever it may be are there for them. It's a bit cute, mostly annoying though.
No my cat doesn't do that. Just a little bit of discipline goes a long way. Lines have to drawn otherwise like children they will not learn. It's for their own good. You don't want them doing that when you have visitors.
@pumpkinprincess: Don't worry they will still be silly in other ways. They're cats. I allow my cat to go anywhere she pleases except on tables and kitchen counters. She also respects my food and my tea or whatever.