Tekashi69 Beefing with Slim 400 at ComplexCon, Ditches Event

Tekashi69 still can't open a few doors -- the rapper and his crew walked away from ComplexCon after Slim 400 started beefing at the entrance -- and Tekashi was PISSED!!!

We've obtained video of the showdown between 6ix9ine and Slim 400 and, as you can see, there was no love lost between them -- just tons of hostility and insults being hurled every which way.

You see Tekashi rolling deep Sunday night to the Hyatt Regency in Long Beach. His crew was immediately confronted at the door by Slim 400 and his squad, and the tension mounted while both sides yelled back and forth.

Tekashi had to be held back, but eventually chose to walk away. Pretty amazing when you watch the video, because it definitely feels like violence is about to go down.

6ix9ine and Slim have been feuding for months. We're told Slim's crew was posted up outside the door as if they were waiting for Tekashi's arrival. Sources close to Tekashi tell TMZ the rapper was livid after he was invited to perform at the event, and was met by Slim and his squad instead of proper security to escort him in. He chose to walk away from the whole performance, rather than risk things escalating.