Drops Kim Jong-un Bomb Joke

... at Bruce Willis Roast

Dennis Rodman went nuclear on Bruce Willis at the Comedy Central roast -- and he used his friend Kim Jong-un as a punchline.

Everyone knows how seriously Rodman has taken his relationship with the North Korean dictator over the years -- but when Dennis took the stage, he targeted Bruce with a bomb joke.

"Bruce, you keep making these f*cking bombs. Well, guess what ... So does Kim Jong-un. But at least Kim is smart enough not to release his."

It wasn't the only time Rodman referenced his dealings with North Korea -- he also told Martha Stewart the next time she gets locked up, he can help secure her release.

Dennis also dropped some penis, vagina and stripper jokes ...…