South Park: The Stick of Truth - Friends in Strange Places Achievement

Achievement - Friends in Strange Places
Befriend Crab People and Underpants Gnomes.

To befriend the Crab People, you must acquire the final fart spell, Nagasaki, from Terrence and Phillip in Canada. Then you must go all the way to the end of the sewers and break the rock with your Nagasaki. This will clear the path to the Crab Person, who will friend you after talking to him.

To befriend the Underpants Gnomes, you must complete their side quest to find 5 pairs of underpants. The underpants can be collected at any time, however the sidequest with the Gnomes only becomes available after you finish the story quest related to them at the start of Day 3. The underpants are located:

1. In Cartman's room
2. In Stan's room
3. In Stan's parents' room
4. In Kevin Stoley's room
5. In Kyle's room (must progress in the story)