Refers to the involuntary "geyser" of liquid/slurry that one produces when something funny/shocking is spoken in his presence while he's eating/drinking something, said utterance causes an "automatic" or "uncontrollable-on-short-notice" lung- expulsion from a laugh or cough, which in turn causes a forceful ejection of the mouth's contents which shoots out for several feet and disgustingly messes up anything (or anyONE) in its path.
A classic example of a "firehose" remark-reaction is when Jimmy Culp does an astonished "sploooot!" when he hears his name mentioned by Robert Stack on the Tonight Show immediately after taking a deep swig of beer.
by QuacksO February 21, 2019