Asshole is a vulgar (dirty) slang word. Besides the literal meaning, it’s a common word for a jerk or idiot.
If you call someone an asshole, they're probably doing something not just stupid and annoying, but mean. Like all slang words and obscenities, this is a word you need to be careful about using. Saying asshole in class, in a paper, at a job interview, or even on television could get you in serious trouble. If you’re not alone with your buddies, stick to a safer word like jerk or doofus.