Logan Paul and KSI Have Heated Exchange at L.A. Nightclub

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 L.A. nightclub Wednesday night.

The YouTube superstars will go after each other at a major news conference this Saturday at the L.A. Coliseum to promote their superfight in Manchester on August 25 ... 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. I really can't miss. I literally can't miss. Dawg, your head looks like a hot air balloon. I can't miss it."

KSI: "Just wait 'til Saturday bro. Saturday bro. Saturday bro. Your mom's going get it, your daddy's going get it."

Logan: "I can literally smell your bandana. It smells horrible. No one's laughing at your jokes."

KSI: "I can't wait to hear your heckling when you gotta shave your head bro. Trust me."

Logan: "I hear crickets, bro. That wasn't funny. You're not funny, you can't box."

Logan: "Look up to me, bro! Look up to me! Yeah, bro. Take a swing at me on the 25! August 25. August 25."