Green’s Dictionary of Slang

(orig. US campus) disgusted, repelled, appalled.

1966		Current Sl. I:2 3/2: Grossed out, adj. To be repulsed by what someone has said.
1967–8		Baker et al. CUSS.
1991		M. Myers et al. Wayne’s World [film script] He holds up the coin to Wayne and Garth. They’re grossed out.
2000		Guardian Rev. 31 Mar. 5: Grossed-out city yuppie, objecting to roughing it.
2016		T. Robinson Rough Trade [ebook] Or maaybe she was just grossed out.