Green’s Dictionary of Slang

1. (Aus.) to do things in a simplistic manner.

1903

Bulletin (Sydney) 20 Aug. 33/1: Then those papers all would praise us and would say we ‘simped’ no more!

2. (US black) to act like a fool.

1967–8

Baker et al. CUSS 197: Simp Be excessively submissive to your girl friend.