B+M etiquette????

Whenever playing in person, i'll ask to see a player's cards a reasonable percentage of the time when he calls me down and tries to muck them...

i generally get a rude response after a while from both the player or the surrounding players, whether it be comments under the breathe or dirty looks... (keep in mind i don't do it every hand, only when i'm truly intrigued by someone's turn play etc..., or i really really dislike them)

is there some etiquette that i'm missing here??? as far as i'm concerned it is my right, and they shouldn't call down if they don't want their cards to be seen... just wondering if i was being a complete a-hole or not