It is a fairly common practice. That being said, it's a bad idea to allow that to stand in your code base. It never adds anything to the clarity of the code, other than the fact that you now know the developer writing it has a bad temper.

While you're in there cutting out F-bombs, you should probably do yourself a favor and review the surrounding code. Foul language in comments are almost always put in out of frustration, so you probably have some good targets for code refactoring.