The occassiona under which you should not wear tartan flashes would be:

1. Casual attire
2. Black tie events
3. formal attire
4. dog fights
5. Mud wrestling event
6. Any even at which you would see another human being.



You can see that, although I own a pair and have worn them, I do not care for them. But they don't really offend me, so do what you want. But just consider that if you wear standard flashes or ties, no one will object.