I’ve sat around crab feasts where it’s considered rude to not eat whichever (lame) crab you first pull off the pile. If you grab it, you gotta eat it, whitey or not. Usually kids at those tables are scolded for trying to pick the best one.
And I’ve sat around crab feasts where it’s just fine to pick one up, feel its weight, drop it and check out a few more, where it’s perfectly fine to be very selective, even if you have to pick up every crab in the pile to be sure.
My house rules? The latter. We don’t need no stinkin’ rules for eating crabs. Knock yourself out.