DUDE -- You're at a party. In my opinion that's like the easiest place to talk to people because you don't have to be casual, so in most cases you can say just about anything even if it doesn't fit in. Just be crazy and talk about whatever the hell comes up or whatever the hell you want to talk about.
You see a hot girl, talk to your friend about how much you love that ass. (And then approach so you know for sure!)
See a cool movie? Mention it. Someday you almost got run over? Mention it. You wanna piss? Mention it. You think bats are cool, wish you were a dolphin or something? Mention it.
LOL, you're worrying about it too much. It doesn't really matter.
Remember to just say whatever you want! How many things there are in this universe? Bet you have no ideia... that's just how many things there are to talk about.
Oh, and inside jokes are FUN especially if not everyone around you knows what's going on. LOL, it's awesome to turn to your friend and say "Milk", and then suddenly start laughing like crazy causing everyone else to laugh too, even though they have no idea what's going on.
Yeah, tease them if you want. Make inside jokes if you want. Say whatever you want to say, if you want to say it. Even if it's stupid, don't worry about it, just go ahead and have fun!