The process before falling in love with someone, once you have cliffed, you are falling in love with that person. (After you jump off a cliff, you are falling)
Girl A, "Wow! Josh is so cute! I think I'm cliffing."
Girl B, "I know! But Jessica already cliffed for him"
To talk/sing to one's self
He had a lonely time at lunch today. Yeah, he was just cliffing...
Vomiting; throwing up; hurling; puking etc. etc.
More specifically: Throwing up in someone's car.
Background: After eating McDonald's, Cliff threw up all over Max's car, therefore throwing up in someone's car became "cliffing" and then it became a general term for vomiting.
After eating some suspect curry and smoking too much pot, Zak ended up cliffing all over the back of our van.
To go behind someone and to fake hump them without touching them. They must not notice. This was given a name by the infamous Cliff Jia in the summer camp of 2004.
He was just Cliffing you girlfreind