KOURTNEY KARDASHIAN Hey Scott ... HERE'S WHAT YOU'RE MISSING!!

Kourtney Kardashian and Scott Disick are back together for co-parenting purposes ... and it looks like she's giving him a refresher on what he's not getting on the reg anymore.

The ex-couple are on vacation with their kids in Hawaii this week, relaxing poolside with some fresh fruit and drinks. Scott looks like he forgot his swimsuit ... but Kourtney definitely remembered her finest bikini.

Hard to tell if Scott's digging it ... but he should be.