Bad breath, could be harder to control. A bad cough could be sorted in most cases. A bad laugh could be changed, this one funny Family Guy - Girl With A Bad Laugh
I'd go with bad laugh as being the worse. At least the cough only comes when you have a cold, and while bad breath is pretty bad, I'm pretty sure there are solutions for it.
Even I find bad breath...just too much to bear....it is a completely turn-off for me.... Regards, RightMan