Where are the underwear?

I have been around South Park hunting for the underwear as a side quest...Yes underwear...I have 4 of 5 and cannot find the last one. Anyone know where I can find these sets of drawers? Pretty sure I found one in my own house if that helps any, along with at Cartman's house.

Underpants can be found in Kyle's Room, Cartman's Mom's Room, Kevin's room (the Star Trek Kid), Stan's room, and Stan's parents room (the one that most people miss).

Stan's house has a nonstandard floor plan. Across the hall from his sister, there is a 'hidden' door at the bottom of the screen. You'll find underpants in there.

This is related to the Friends in Strange Places achievement. Including that in your question and searches would more quickly give you the answers you seek. Per various sites, but sourcing trueachievements,

To befriend the gnomes, you have to wait until after night two, after the gnome section where you get shrunk down and chase the gnomes trying to get big again. Once you wake up on day 3 the gnome will be in your room and he will give you a quest called 'Phase 1' which is to get him 5 pairs of underpants. They are located at the following locations:

1. In Mrs. Cartman's bedroom in the drawer by her bed
2. Stan's bedroom in the drawer by his bed
3. Stan's Parents room in the drawer by the window
4. Kyle's bedroom in the drawer by his bed
5. Kevin Stoley's bedroom in drawer by his bed, he is the kid that acts like Spock from Star Trek

As per good RPG/Adventure strategy, loot everything as soon as you can. Take everything that isn't nailed down before coming back with a crowbar to get those. By adhering to this mantra, you will find things easier and, in this case, you should have collected all the underpants quest items already (which can't be sold so you wouldn't lose them).

To befriend the crab people for the achievement,

You don't get the Nagasaki fart until you get to Canada and talk to the two "monks" so this achievement is not obtainable until after the middle of day 3 ... Now, to become friends with the Crab People you need to go into the sewers, the access point is to the left of the post office. You need to make your way all the way through the sewers and as far down as possible and you'll come to a point where there's a crab person playing a drum and singing. You need to use the 'Nagasaki Fart' ability on the glowing rock to the right of the crab person, and once you do you can walk right up to him and get a friend request.