Rather crude sexual act, when one defecates in their partner's mouth (the coffee), then cums in it (the milk/cream). Some go so far as to urinate or spit in the mouth as well, although I'm not sure how these work in line with the rest of the 'coffee'. Perhaps they represent sugar, I'm not sure.
Average Joe 1: Ahh man, Becky was annoying me last night, so when I saw she was asleep with her mouth open it was the perfect opportunity to give her a Californian Cappuccino!
Average Joe 2: Did you do it?
Average Joe 1: Nah, she woke up as I was pulling down my pants.
Average Joe 2: Ahh, bummer man.