From Wiktionary, the free dictionary
Literally, “to have an erection like a donkey”.
- IPA(key): /bɑ̃.de kɔ.m‿œ̃.n‿an/ ~ /bɑ̃.de kɔ.m‿œ̃.n‿ɑn/
bander comme un âne
- (of a man, simile, vulgar, sexuality) to have a strong boner, to have a raging boner (to be very aroused and have a strong erection)