In my experience, it's not "normal practice" but it's common enough. I don't like it, not because it's unprofessional as such but because it conflicts with the principle of removing everything extraneous. I think the best code is code that has been distilled to its clearest essence.

Edit: incidentally, profanity in code is not limited to comments. "White Like [name deleted]s Balls" is a variable name I saw once and have not yet had the good fortune to forget. I'll let you guys guess whether this was code distilled to its clearest essence. :)