1. Licking the anus
2. Pleasuring oneself whilst being female
3. Lubing up
4. Literally varnishing a big O which has fallen of the front of a shop and is now serving as an ornament in a gentleman's apartment.
5. Other sexually euphemisms of the readers choosing.
I hope the police don't see me Varnishing the O in the garden this summer, hopefully they won't recognise it if they do!