Boffed is the past tense of boff, slang for having sex with someone: They boffed in the back seat.
The word is casual and slightly comic—less crude than fucked but earthier than slept with.
Boff can also mean to hit or punch, though the sexual sense dominates modern usage.
1. hitting — struck, Past tense of hitting; whacked (Struck forcefully); bonked (Struck on top); smacked (Hit sharply); thumped · walloped · clobbered · clonked · bopped · slugged · bashed · knocked · pounded · socked
2. sexual — hookup, Casual sexual encounter; fling (Forceful toss, or tryst); liaison (Connector between groups); tryst (Secret romantic meeting); encounter · romp · affair · rendezvous · intimate · casual · amorous · canoodle · frolic · frisky