Jeff Bezos and Lauren Sanchez are kissing like there’s no tomorrow -- playing lovestruck teens while cruising to their fairy tale wedding rehearsal in Venice … while all the world watches.

The PDA was full throttle -- the couple were smooching and waving like royalty from their water taxi Thursday, with Jeff grinning ear to ear and Lauren beaming just as hard ... looking surprisingly comfortable for someone dripping in extreme, skintight couture

Lauren was serving bombshell -- rocking a sculpted off-the-shoulder midi with a metallic bodysuit that snatched her waist to perfection. If there was a pre-wedding health kick, it definitely did the job!

Jeff was giving full billionaire swagger -- wearing a sleek suit, crisp wedding shirt, and looking every bit the mega-rich groom-to-be as they made their grand glide through Venice.

Of course, the A-list crew -- including Orlando Bloom, Tom Brady and more -- were also hopping on water taxis, ready to kick off the ultra-glam wedding weekend.