I do that to people I know well if they are shooting off at the mouth and being stupid/mean to people and need to stop
Example: a friend was sitting w/ boyfriend and I at a bar and making mean/rude comments about the bartender's physical appearance. Two other friends there were feeding his little comments by laughing and playing along with him. After glaring at them then telling them to stop, and nothing happening. I just reached over and covered his mouth. The bartender was a really nice woman and an excellent bartender and I got tired of them talking about how she was fat/how they wouldn't want to have sex w/ her,/etc and I KNEW she could hear them.
I think Kelly probably just flipped out 'cause she doesn't know Clay and she seems pretty high-strung