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'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

I use it for "disconcerted", but I guess any situation that would result in a diagonal mouth irl would be fine.