For the challenge, all you have to do is slink out into the environment and find either a dumpster or a bale of hay and hide. To use one of the hideouts, all players need to do is find one, walk up to it, and then interact with it. There are multiple hideouts around the map.
Players will need to hide in a hideout in three different matches to complete the challenge. For hiding in dumpsters, Oscar the Grouch style, the best places to look are around the back of buildings in locations like Retail Row, Sweaty Sands, Dirty Docks, and so forth. If hiding in the trash isn't your thing, head to the rural parts of the map and search out bales of hay.
You're specifically looking for the big round bales of hay that you can find at places like Frenzy Farm, not the small ones you may run across on the map. It's worth noting that you don't want to slip into a hiding spot while an opponent can see you. They can kill you by destroying the hideout while you are in there.