Nothing says "friendship" like 3 guys on a banana boat ... with Dwyane Wade's wife.

Here's (in order) Gabrielle Union, Dwyane Wade, Chris Paul and LeBron James cruising around the Bahamas ... with a giant inflatable banana between their legs. Fun!

We're told the gang spent 3 days hanging out and partying together ... riding jet skis and splashing around in the ocean ...off the side of the mega-yacht they were all staying on.

The real question is ... who's recruiting who?