Bill Bellamy -- Ken Griffey Jr. and Isaiah Rider DUNKED ALL OVER ME

If someone's gonna posterize your ass on national TV ... it might as well be a former slam dunk champ coming off an assist from Ken Griffey Jr., so says Bill Bellamy, who actually speaks from experience.

It all went down back in the early 90s on "Rock N Jock" -- that MTV show where entertainers played sports with pro-athletes -- when Bill says Junior dished a pass to ex-NBA star Isaiah Rider, who then "jumped over [him]" to throw down the jam.

So how do you bounce back from that kinda on-court shame? You don't ... but check out the clip to see how Bill handled it -- and here's a reminder of Isaiah's dunking prowess.

Ladies and gentlemen, the legendary "East Bay Funk Dunk" ...