I only get irritated when somebody goes for a killcam that isn't good. For example. Score's 3-3, it's 2v1 our favor, our guy sees the last guy on the stairs to the helipad, defense side. He's one of those people that needs to stand still and the guy isn't even moving. He double y's for some reason or another, misses, does another double y quickscope, gets a hitmarker, and the guy sprays him down with a UMP. He then proceeds to yell in the lobby and complain about hitmarkers.
The killcam would've been bad no matter what you did. Had you hit him in a vital killpoint, you wouldn't be getting the hitmarker.