2. A man that's single who masterbates frequently. Usually a loser type guy. This term was brought from the idea of the penis being your wife and beating it...well you get the picture. Another fun way of using this term is by saying "Im gonna go home and beat my wife!"
2. Look at Carl, he's such a wife beater.
I think the TV show "COPS" had a lot do with the creation of this word. Every time they showed a guy getting arrested for beating his wife he was wearing one of those sleeveless undershirts.