have a hard-on for (someone or something)
1. vulgar slang To desire someone sexually. Typically said of a male. "Hard-on" is a vulgar slang term for an erection. I heard you have a hard-on for the new girl—is that true?
2. vulgar slang By extension, to have a strong desire or affinity for something. Chrissy had a real hard-on for that band, but now she thinks they're sell-outs.
have a hard-on for someone
tv. to wish to do someone physical damage; to seek revenge on someone. (The aggressor and victim are usually males. Usually objectionable.) The punk thinks he has a hard-on for Mr. Gutman.