One who pulls ridiculous faces whilst under the influence of drugs such as E's, Coke, Speed etc.
Can be characterised by excessive jaw motion whilst hammering a piece of chewing gum, wide eyes and a streched out gob contorted into numerous positions.
Can also be used to refer to those smashed out of their tiny little trees on top quality skunk.
1. Look at that fellow, he's a gurning drug monkey...
2. We don't want to walk around Amserdam with a bunch of gurning drug monkeys