It's actually pretty hilarious ... the ring does look like something outta a gumball machine rather than a celebration of nearly winning the NCAA Tournament -- and Hart couldn't believe it.

"This weak-ass ring!" he yelled at Mo ... "Thing weak as hell!!"

Hart continued ... noting the lack of shine in the diamonds, saying, "They fake as hell! This is what happens when you a runner-up. This what you get!"

To his credit ... Wagner took it pretty well -- though he did beg pretty hard for Hart to stop the initial clown down from happening.