A frient with benefits is a friend with whom you enjoy marijuana (friend + ent) and occasionally get partially/fully naked or whatever. Need not include sex.
Dude I'm so stoked to have met Jolie, we had a blast Saturday night getting blazed together, went for a walk in the rain, and then we ended up getting naked at my place. The next morning we had coffee on my porch and she's like "that was really nice, we should do it again soon." I'm so glad to have a frient with benefits!