Monkcheese is a word used to insult somebody or to describe their nasty smell.
Monk = from monkfish: smelly and a stupid fish
Chesse = very smelly and dense in substance
Boyfriend has just been for a run and stinks ....
"Yuck you smell like MONKCHEESE!"
Friend has just fallen flat on their face in public .......
"Get up you MONKCHEESE!"