Blac Chyna -- Bad Ass Pitch Woman for Rob's Sox (PHOTO)

Blac Chyna should not be Rob Kardashian's first pick to pitch his sock line ... because the distractions are overwhelming.

Chyna posted this pic, wearing little else butt a pair of Rob's Arthur George socks.

Meanwhile, back at the ranch, Amber Rose posted a video with the caption,"Drunk af #trinidadcarnival."

They're still in Trindad ... they like to party.