Logan Paul and KSI just couldn't wait 'til this weekend to start letting the insults fly ... getting right in each other's faces at an LA nightclub Wednesday night.
The YouTube superstars will go after each other at a major news conference this Saturday at the LA Coliseum to promote their super fight in Manchester on August 25th ... but gave a preview of their smack talk when they ran into each other last night.
Some of the highlights ... (warning, there's a LOT of "bro" going on)
Logan: Your head is the size of a watermelon.