Aimee Ault from deviantART discovered that some of their stylesheets would fail to load for some users. Turns out those users were
accessing the site from computers with overly sensitive system-wide profanity filters installed. These users' browsers likely stopped parsing the stylesheet entirely upon reaching the word in the stylesheet, leading to a fairly ugly and/or broken page.
Ideally you have a build system that compresses CSS and removes comments, but if for whatever reason you ship CSS with comments in it, don't swear.