YouTube superstars KSI and Logan Paul showed off their maturity and high respect for each other at their boxing rematch news conference in the UK on Monday.
Juuuust kidding ... there were tiny penis jokes and jabs about dead pet dogs.
The rivals met up in London on Monday to promote their upcoming rematch at Staples Center in L.A. in November ... and shocker, it basically turned into a roast.
KSI was quick to bring out the props -- with a 4-legged friend that looked just like Logan's late dog, Kong, who was tragically eaten by coyotes earlier this year.