Scott Steiner is calling BS on Hulk Hogan -- claiming he never threatened to kill the guy before WrestleMania ... and says Hulk's just acting like a scared little bitch. 

We broke the story ... Steiner is under investigation over a March 26th encounter with Hulk's wife Jennifer -- when she claims Steiner grabbed her at the San Jose airport and told her he was going to kill Hogan. Jennifer and Hulk filed a report with police the next day. 

"I'm not going to dignify [Hogan's] lies," Steiner said ... "I didn't put my hands on her."

Steiner says he did approach Jennifer that day -- but only to talk some serious smack about Hulk introducing "Macho Man" Randy Savage at his WWE Hall of Fame ceremony.