Are these returnable?

I assume if it's unopened, you may be able to return it. You must read Amazon's return policy.

I am a male with around a 36" waist. Will these feel good and what size should I get them in?

They are very soft and comfortable and size 10 should fit you as far as your waist size is concerned, but there probably is not enough room to overall to fit your many parts.

does the leg opening have elastic?

A quick looking at and stretching of the leg opening indicates the Hanes Women's Briefs I purchased do have elastic leg openings. The fact that I purchased along with the Hanes briefs Vanity Fair Lollipop briefs supports this, as I had been shopping for elastic free leg opening briefs and opted to buy the Hanes briefs because I was simply in need of briefs. The Lollipop briefs have a cuff leg, which as I understand means the leg band is of the same material as the briefs, not elastic I hope this is of some help to you.