Charlie Sheen -- Ashton Kutcher SUUUUCKS

And now a torpedo of truth from Charlie Sheen -- "I'm tired of pretending Ashton doesn't suck."

Sheen called in to TMZ Live today ... when he finally spoke his mind about the guy who took over the starring role on his old show, "Two and a Half Men."

Sheen had been politically correct towards Kutcher ever since AK took over ... but after Warner Bros. legally threatened Charlie for using a "Men" photo to promote his new show, "Anger Management" ... it was no more Mr. Nice Guy.

Sheen told us, "I'm tired of lying ... I'm tired of pretending the show doesn't suck ... I'm tired of pretending Ashton doesn't suck."

Charlie added, "It's nothing personal ... I just feel bad for him ... he's saddled with such bad writing."