1. noun - person unable to eat or pour liquids without spilling half the contents down their front
2. verb - to unsuccessfully attempt ill-advised transfer of liquid or semi-liquid foodstuffs from one object to another; to eat messily
3. adjective form "slittery"
2. Don't try and pour your tea into another mug. You'll slitter half of it for sure.
3. Aw ya big slittery monkey. Look at the mess you're making!
The person doing the slit work is the slitter.
"All this guy is does is work, he has no life he's miserable! What a slitter.