One of the dirtiest insults in English. It names a man by a sex act in order to put him down hard. Do not say it, write it as a joke, or try it to sound tough — people may think you want a fight, or they may freeze in shock. It is mainly American, mainly aimed at men, and much heavier than idiot or jerk. Some people throw it around as a loose “I hate you,” barely thinking of the sex meaning; that does not make it safe. It has often been used to shame a man as not “man enough,” including cruel talk about men who love men. Even among friends it belongs only in the roughest rooms, and it can still explode.