Wearing sweat pants is a good idea for many occasions, including weddings, funerals, and lounging around the house. When wearing sweat pants I would advise two things: wear underwear and make sure your sweat pants are pulled above your waist.
A certain person who I live with unfortunately routinely disregards these rules. One of my roommates nabbed pictures that showcase a complete lack of sweatpant-wearing judgement.
Exhibit A
Exhibit B
If you're going to wear sweatpants, and God knows you should, please do not fall into these traps. And, in particular, don't sit on my couch (Exhibit B).