Paulina Gretzky -- Engaged to Dustin Johnson ... Men Everywhere Depressed

As if the world wasn't bad enough ... smokin' hot Paulina Gretzky has dashed the hopes and dreams of men worldwide ... by getting ENGAGED to pro-golfer Dustin Johnson.

Paulina announced the terrible news on Instagram Saturday -- posting a pic of the giant diamond rock on her ring finger, captioned "Never been happier."

The couple has only been dating since early 2013 -- but, really, who wouldn't lock that down?

Now, a final farewell, to Paulina's almost-hitched assets ...