Not accepting food and drink from a household you’re visiting.
Insisting on paying your own share of the meal (if not taboo, certainly frowned upon: you have to at least pretend to offer to pay for everybody).
Failing to use formulaic expressions (“Happy month!” “Happy business!” “May she live long for you!” “With health!” “Life to you!” “Take this guy to your wedding, and he’ll wish you many happy returns!”)
Waiting your turn in a queue isn’t a taboo, but it does mark you out as maladjusted to the social realities there. Even if there is a proverb encouraging it. (“Even if you’re a priest, you’ll go to your line”)
No taboo about blasphemy: cursing in Greece really is still cursing.
Ethnographically, I think there is still a taboo about dropping bread to the ground. It was enforced by the legend of how Hagia Sophia was inspired by Justinian dropping a crumb of communion bread to the floor, a bee flying off with it, and fashioning a mini Hagia Sophia of wax with the crumb at the altar.
Praising people too vocally, especially if they are babies. Ritual spitting ensues to ward off the evil eye. That is probably on the way out.
Saying nice things about Turks. That’s probably starting to be on the way out too.
Saying nice things about Angela Merkel or Wolfgang Schäuble. That one’s definitely on the way in.