Fat experiences

So, turns out there are some struggles with being 400+ lbs. One of the most annoying ones is that my underwear tends to ride down when I walk. They fit over my (rather big) ass and I can wear them normally, but as soon as I walk for more than a few steps, they slide down. I wear boxers and I'm wondering if it's my thighs pulling them down, or that men's underwear simply aren't made for a body type like mine. If anyone has any advice or want to commiserate, please do let me know.

When I started putting on weight, I began wearing men's thongs, which I consider the best option for heavier guys. Jockstraps and briefs are fine too, but you have to get the right cut. Boxers are the worst.