Simp

This is a term from the early 80's.
SIMP is a derogatory term, short for SIMPelton, and is used to refer to someone that is lacking in mental capacity.

OMG! You can't be serious, you are such a simp!

Simp

From the early-mid 80's.
Short for "Simpleton"
1) A person lacking in basic 'walking around sense'
2) Another way of calling someone a retard/idiot

Bill is such a simp, he probably can't even dress himself.