A quick glance in the mirror is permissible, but absolutely don't spend a significant time arranging hair, clothing, etc. Zit popping is only permissable after checking to see nobody else is around. No profanity of any kind. This is reserved for locker rooms, only. If you must wait, form a single-file line, ragged, and be sure to keep looking around.
All graffiti is anonymous.
If there's any chance somebody can trace your graffiti back to you, don't do it. Writing graffiti in the open section of the bathroom is only acceptable if nobody can see you. Writing in the stalls is similarly acceptable. If the bathroom is used by a small few, restrain comments to amusing anecdotes or chit-chat about secretaries. If visiting dignitaries from other companies or the government may tend to use the bathroom, graffiti is forbidden.