The squeaky-clean Patrick Mahomes may have finally misstepped ... 'cause according to Henry Winkler, the Chiefs superstar has inexplicably left him hanging on a sweet dinner invitation.

The Fonz relayed the surprising news to TMZ Sports while signing some autographs in Los Angeles this week ... saying despite initially agreeing to come to Winkler's pad for a homemade meal, Mahomes has now ghosted.

"I think he fibbed to me," a defeated Winkler told us.