What to say to guys at parties?

i never know what to say to guys when they come up to me at parties! for example, one night i was leaving a room and there was a guy next to the door in the hall and he stood in front of me with his arms out. i just said 'what' and he just said 'hug' so i gave him a hug and when i let go he gave me a booty bump and i didn't know what to do next so i just left to find my friend. he was completely random, i only kind of knew his friend because he was running the keg and he started talking to me. stuff like this happens a lot and i feel like i come off as snobbish or something, which i'm not, i just don't know what to say because i don't want to say something lame haha. so my question i guess is what would you say in these situations? either the one i told you or just in general, thanks so much!