ALT 2: To masturbate
Sexual euphemism reflecting media clusterfuck around Christine O'Donnell, bizarre non-sex lobbyist who is/was the teabagger 2010 Republican US Senate candidate in Delaware.
Considering 1. his presence every time you're messing around with her (surely the library, the living room, or your room would've occurred to him if he were uncomfortable being in the same room while you fingered / O'DONNELLED his girlfriend) and 2. the limitations she's placed on the sex she's willing to have with you, and 3. his tendency to suddenly "show interest" after you've been messing around with his girlfriend (at which point you "move over" and, presumably, out), I'm thinking your girlfriend's primary partner has a bit of cuckolding lite/sperm competition syndrome thing going.
person 2: "Really? how big was it?"
person 1: "I dont konw, but it mus have been at least 2 Rosie O'Donnells."
person 2: "Holy shit, 2 O'Donnells?!"