How do I get my dad to wear pants during the day when people are present?

I'm assuming someone is actively trying to help him put the pants on and not relying on him doing it himself...

Does your dad have difficulty zipping or buttoning the pants? Try sweatpants or something easy on/easy off. (adaptive clothing)

Do the pants fit him (i.e. do they droop and require a belt)? Try suspenders or easier w/elastic wasteline.

Lay out 2 pairs of pants and letting him choose which one to wear.

FYI there are sites online that sell "adaptive clothing" for people with dementia/ALZ. Good luck!