Is it ok to send a boy to preschool without underwear?

We got back from a vacation Sunday night and I had no time to do laundry. Monday morning after getting my son out of the bathtub I realized he had no clean undies. So he wore a T-shirt and just sweatpants to school. He's OK with it and now prefers no underwear but the wife is pissed and thinks he should have stayed home.