The yellowish liquid that comes out from an upside down mustard bottle right before you squirt mustard onto a food item. Usually groans can be heard from the squirter indicating that mustard pee came out of the bottle instead of mustard.
by Cannibalporsche July 2, 2011
Mustard pee- That undesirable yellow liquid that comes out first when you are really expecting mustatd and usually makes your sandwich soggy
I made a sandwich in the middle of the night. I wasn't awake and forgot to shake the mustard so all he got was mustard pee that made his sandwich all soggy.
by IvyDana55 August 27, 2017