(v.) To use one's index and middle fingers to slap another in his/her neck. (n.) The act of flumhumming.
The word comes from the game of Musolum, a game in which players say a made-up word in an attempt to catch others off guard. If the recipient of the made-up word responds with any word such as huh?, wha?, hmm? or whadjoosay?, the recipient is then flumhummed.
Note: Flumhumming is not the same as musolumming. Musolumming is initiated by an intentionally misspoken word, whereas flumhumming can happen with no provocation or forewarning.
Ha! Flumhummed you with the key to my car! That's gonna leave a mark!