Misspelling of отстой, which means “sediment” but has gained the colloquial meaning “bullshit, crap” (the words carries a notion close to “left over, discarded”). Sometimes written ацтой, атстой.
Адстой! Хоть и интересная идея, но адстой!
Bullshit. A great idea, but bullshit.
(Ranta May @ mobbit.info, 08/2007)