Bubba Watson -- I'm the KING of Mini-Golf ... Watch This Insane Shot!

Happy Gilmore ain't got NUTHIN' on Bubba Watson ... at least, when it comes to putt putt golf -- and Bubba shot a crazy video of a trick mini-golf shot to prove it.

The 35-year-old PGA champ was at the Fantasia Gardens and Fairways Miniature Golf at Walt Disney World in Florida when he decided to play one of the holes ... backwards.

Basically, he shot from the tee at one of the holes .... into a cup from a previous hole.