I suppose your guess is as good as mine on the "grab his butt" bit. He doesn't like clothes to touch much; tags are another thing. He's not overweight, he's not tall, so... Neither of us really understands.
There's ONE brand/style of long pants he will wear, and they're long discontinued, so I get them cheap on eBay. Polo Ralph Lauren "Hammond" pants, only in "tissue" weight, and only those manufactured in Singapore, Macau, or Indonesia. Even then, sometimes they aren't okay. Can you tell it's a little frustrating?