Here's Warriors big man JaVale McGee Shaqtin' a fool on horseback -- 'cause life is good after you re-up with one of the greatest NBA teams of all time.

The Dubs officially completed their 2017-18 squad by bringing back JaVale on Thursday ... and the 7-footer celebrated by riding around on what looks to be a pony -- but that's only 'cause JaVale's HUGE.

McGee signed for the vet minimum (less than $3 mil) ... but dude's clearly pumped to be back in the saddle with the superteam. 

More proof:

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