The term refers to the solitary conditions faced by inmates in Guantanamo Bay where they would be locked up for 23 hours a day with no interaction with other detainees. The difference between the inmate and an Omar skanker is that an O skanker has a choice.
Person 2: He is pulling an Omar skank, ruining my holiday too!
Dude 1: Is there something wrong with him? he seems to be locked up in his room the entire time we have been here. He also claims to be sick yet I've seen him chugging that liquor in there
Dude 2: i think its all a load of shit and we're being skank'oed.