I've been to a few meetings in my working life, and I have come up with a few DON'Ts list. Do NOT:
1. Pick your nose
2. Shake your head for dandruff
3. Scratch your hairy leg and then flick the stuff away from your fingers
4. Scratch anything, period
If you are attending a meeting and one attendee displays the above traits, do NOT
1. gawk with mouth wide open
2. say "eeeeuuuuuu!!! have you NO MANNERS???"
Instead, I believe, the thing to do is to keep very far away from this person.
Yes there has been such meetings and there are such people. Believe me.