What does it mean when people say something in a cough?

this is probably a stupid question ^_^;;. what does it mean when people say stuff in a cough, like idiot and stuff? there was this really jerky girl at school who used to always do that and i just gave her a wtf face and walked off, but i never knew what it meant. i feel so stupid... but the girl got expelled about a month before summer break so i guess it wasnt just me. i heard she gave a girl amnesia by hitting her too hard on the head... im glad im taking tae-kwon-do again lol