I haven't owned that kind of fish, but from my humble opinion, I would say that the fish is either loopy, or attempting to get rid of some kind of parasite. Or it could be his method of begging for food, but I doubt it.
If this popeye isn't bacterial, you should consider doing a couple largish water changes - that would also get rid of some parasites, if they are free floating in the water.
Sometimes, you just have to buy a fish.
Sometimes, you really shouldn't