n., 1) an unattractive or undesirable woman with whom one has a surprisingly energetic or satisfying sexual experience. Intended as complimentary; 2) also, the sexual experience itself. (After Giuseppe Garibaldi, Italian revolutionary and paramilitary leader who conquered Sicily and the defeated the Kingdom of Naples with only 1,000 ill-equipped troops. Also refers to n., "bald", poss. pertaining to a shaved female pubic region.)
Ethel is no hottie but she's a garibaldi in the sack.
What are you up to tonight, Bob? Trawling for a garibaldi at the club?