comes from the word gamisi (fuck). is the person that fucking all the time.(both ways)
similar to word fucker.
also used for a scammer.
mas tin ekane o gamiolis
(he scummed us the gamiolis)
aaa aytos einai megalos gamiolis
(aaa he is a big gamiolis (fucks and get fucked all time)
means everything is fine.
i agree with the ola kala option for the ok word was born.
In ancient greece, when they load ships with cargo, when tey check the cargo, (always placed in big vases,amphoreis), at the top of each vase, after sealing it they marked it with 2 letters. O K. that means Ola Kala.
everything is fine. so the vase was ready to "travel" in the cargo ship.
Many of those vases where found at greek shipwrecks in the deapths of seas, during ages.
But there are many other options, how the word ok was born, very intresting and worthly to investigate.