We used to use a shit-ton of £1 shower gel - lemon one. It does take some cleaning however and you still feel 'greasy' afterwards (not to mention nutty).
Washing up liquid will work better, but it's horrific for your skin and eyes.
I've covered Mrs FB from head to toe in peanut butter mixed with Nutella. She had to shower for about an hour with lots of shower gel - that did the trick
On a more practical note - Anything like that will yield most easily to Dawn dish washing soap. We used to buy it in gallon jugs for certain applications.
The other methods are in the 'look before you leap' category.
1. lightly coat the area to be peanut-buttered before applying the PB. It will come off easier.
2. Mix in honey or jam with the PB before applying it.
3. Use natural peanut butter. The non-homogenized versions will allow you to add more peanut oil. Using as much oil as possible without interfering with its messy qualities will make it easier to clean off. Peanut oil yields to high quality dish detergent. Maybe there's a variation on Rock/Paper/Scissors to be had here?
And a couple of other tricks - If you can apply baby oil to the intended surface before you gunk it up then cleanup is a lot easier. Not always practical to do but something for the right situation. Hair conditioner was something else we used to purchase by the gallon. Rubbing a double handful of that in your hair during the shower loosens up a lot of stuff too. You'll frequently see that conditioner jug in one corner of a lot of shower photos.
i always have dawn and a giant bottle of conditioner and bring a brush, and those sea sponges? are awesome for the shower.
but, with hair like mine? it doesnt matter how much i brush, condition and use dawn....its gonna smell like pb and dish soap for a couple days. lol.
people ask about the mehron in the eyes. nothing hurts worse than fucking dawn dish soap in your eyes!! shoooo weeee BUT it will break it up. sea sponge and dawn and a steady stream and turn that hot water heater on HIGH BLAST!!! you will need it!
My contribution is Lava soap (usually liquid rather than bar). This is the gritty sandy stuff you use in mechanical shops. It will get anything off your skin. But you will definitely need lotion/moisturizer afterwards because it will dry you out.
I have not used PB but have used Crisco and petroleum jelly. This made cleanup easier. 1. Get a plastic spatula, the kind you use in the kitchen, and scrap it off. The smooth plastic will not harm your skin. 2. This is the time to sacrifice some actual towels. Use old ones or course, or buy cheap new ones. The fibers pick up lots of residue. 3. As for hair, resign yourself to looking like an extra in a 50's movie.