If you've ever known a man who can't keep his eyes off every single woman who walks by, you can call him a womanizer — especially if he's constantly handing out his phone number.
A womanizer is a man who always seems to have a new girlfriend, and who has no hesitation about starting up a new relationship before he's ended the last one. Usually, these relationships are sexual and don't last long. The noun womanizer comes from the verb womanize, which originally meant "to make effeminate." By the late 1800s, the meaning shifted to mean "to chase women."