I'm not sure what the :/ implies, but if you're disappointed by your own folding techniques, spend a bit of time on it, look up some guides, and fold clothes with purpose. or something.
(Rise up against the machines! Folding your own clothes is an act of resistance!)
I use it for "disconcerted", but I guess any situation that would result in a diagonal mouth irl would be fine.
I've always taken :/ to be a kind of hopeless dejection mixed with apathy. In this case, it seems to convey their disappointment in their skills as well as the futility of improving