This occurs when someone may accidentally choke and spit out whatever it was they were eating or drinking. It comes out of the mouth in a strong blast and could possibly land on someone else if they were close by. This may also occur when trying to shotgun hits from a bong or joint with someone else and the person who inhales begins choking on the smoke while trying to transfer the weed cloud to the mouth of the other person. This is not very pleasant and will bring embarassment to the unfortuante soul who does this, but a good friend will usually joke with you about it even though it was gross.
"Oh man, I started choking on my drink and muzzle blasted it all over my boyfriend!"
"Eeuww, gross! Was he mad?"
"Not really, we joked about it later since it was pretty funny."
(inhaling bong smoke, starts choking while shot gunning it to friend)
"Dude, wtf!!! You just muzzle blasted all over me!!"
"Sorry man, I just lost all control when I hit this thing!"