do you ever get stuck with verbal comebacks

well not really verbal in this case but when someone challenges my arguments online...i often get stuck for things to write back at them? my mind goes blank and i can't think of words to put...then i get wound up and frustrated...and in certain times i slammed my fists on the desk in front of me because that person who insulted me or challenged what i said, has gotten the better of me.................and i know i can't be threatening towards them otherwise it's me who gets in trouble.

any thoughts on this or ideas of what to do in this situation?