Big Shaq got TURNT ALL THE WAY UP at a rap show in Oklahoma City -- getting onstage and headbanging along ... while a jacked muscle dude joined the gang and started flexing on the NBA legend.
Sounds weird, we know ... but it's really funny.
Backstory -- Shaq was hanging out at a bar when rapper Chief Peace took the stage during an open mic night and performed his signature song, "Hippy Kid."
Shaq LOVED it -- joined the guy on stage and started dancing away. Some buff guy joined the gang and took his shirt off for some reason.