you guys don't get it? Ok those examples I gave is bad examples.
Why it is NOT polite to ask is becase if you tell them you are wearing size pant, for example, 40. They'd know if you are thin or fat. Why do they need to know if you are thin or fat by telling them what pant size you are wearing?
Suppose some people reading here about sizes and they are feeling uncomforable about it and you know it does affect their self-esteem, I'm not saying it affects everyone but some of them do. I think you shouldn't bring or questioning their pant sizes because again its not manner to ask.
Would you be asking them how much they weigh? NO? Why not? Its same concept as pant sizes. Please be considerate of others. 
Well shrugs 
