A noise, pronounced as a kissing sound, used to confuse, startle, or otherwise fluster an enemy. The "mmfphvtt" sound is often accompanied by a fake ball tap in order to enhance the effect and further annoy the target.
Guy 1: Hey can you help me with this math problem?
Guy 2: Mmfphvtt!!!
Guy 1: God damn it Buckley, my math final is tomorrow!