I have the opposite strict rule: use as many curse words in comments, variable names, and dummy accounts as possible. That way you'll find out quickly when someone else notices!

I recommend against that. :) A team I was on had a demo for a client, and a shaky database schema. I had used, as a test account, the username "MOTHERFUCKINYEAH" for the same purpose. The purging of this account caused a few 500 errors, and we almost lost the client, and although I didn't get fired, we were all shuffled around after that to less critical projects, and one of us actually got sent out of the state.

I don't think they're useful for variable names, but I use them (very sparingly) in comments. A great way to spot what needs refactoring is to find the piece that caused the most frustration to the author. Under a tight deadline, apologies to future maintainers can also be helpful in injecting some levity.