Canelo Alvarez is pissed GGG publicly blasted him as a longtime steroids user -- and the Mexican boxing star is firing back with some good ol' fashioned American trash-talk.
"I'm gonna kick your f**king ass ... little bitch," Canelo wrote on social media.
Alvarez ain't just talking ... he's also showing Gennady Golovkin how he plans to do it with some lightning-fast shadow boxing!!
FYI, GGG destroyed Canelo in an interview on Wednesday ... saying his tainted beef excuse was a bunch of BS -- "It’s not Mexican meat.