After I Fight Yancy Medeiros

Donald "Cowboy" Cerrone says he's slammin' beers and puffin' pot with Yancy Medeiros after they get done scrappin' at UFC Fight Night: Austin ... and he's 100% serious.

You see, unlike some brutes in the fight game, Cowboy tells TMZ Sports he doesn't hold grudges with the guys he goes to war with.

In fact, he does the opposite -- he bros out with 'em!

So after they throw down in Sunday's main event ... Donald says he's trippin' out to Yancy's home state of Hawaii to try some of that sweet, sweet island ganj.

Bonus: Cerrone gives us proof that he's a real-life Cowboy -- showin' off the entire fleet of Harleys he brought to Austin, "MTV Cribs" style!!