"Meen" is what many Suethors, the ones who see no difference between constructive criticism and flaming, call people who offer concrit. It is presumed to be a misspelling of "mean."
It may also be used to satirize the behavior of somebody who is complaining, whether because it is funny or to halt Serious Business. As with any fangirl term, though, using it accidentally or seriously may result in odd looks from your fellow PPCers. Not to be confused with a certain intense green colour on the Sue Colour Spectrum.