Fetty Wap -- Olive Garden Is Lucky I Paid Anything

Fetty Wap was like, "Hey, what's up? Hello," at an Olive Garden Thursday night ... and then he bolted without paying the bill.

Fetty was dining with a group of friends at the famous franchise in Wayne, NJ when he stormed out of the restaurant.

We're told he threw down $100 for the apps and drinks, but by the time he left, the bill swelled to $160 ... possibly leaving the server on the hook for $60.

Fetty says he was there for 2 hours and the service was so slow his food never came, so he said "arrivederci."

But Olive Garden employees say he was there for only 30 minutes and it was a simple case of dining and dashing.

Happy ending ... the server didn't have to pay.