Deontay Wilder -- Tyson Fury 'Crossed a Line' ... It's Time for an Ass Beating

Heavyweight boxing champ Deontay Wilder is sick and tired of Tyson Fury -- telling TMZ Sports the guy needs to stop running his mouth and FIGHT HIM already!

Fury has been trashing Wilder all over the media -- even threatening to sexually assault Deontay ... it's pretty insane stuff.

Wilder says Fury "crossed a line" -- and now he needs to be dealt with ... IF he beats Wladimir Klitschko next month.