I think the anti-Americanism dates back well before the 1980s. The US government was friendly to the colonels during the dictatorship of the late 1960s and early 1970s, and the US did nothing to stop the Turkish invasion of Cyprus in 1974. My guess is that anti-Americanism dates back even before that as part of general European anti-Americanism (Vietnam War and other issues).
It’s possible that the anti-western attitude of many Greeks dates to December 1944. Here’s a story which may be interesting in this regard:
https://www.theguardian.com/world/2014/nov/30/athens-1944-britains-dirty-secret
Also, note that Manolis Glezos, mentioned in the story, was imprisoned and sentenced to death by the US-backed government in 1948, though the execution was never carried out. Glezos is an icon of anti-Nazi Greek resistance in WWII, still alive, a member of a parliament until mid 2015, apparently still writing. It’s as if Nathan Hale had escaped death and was still and alive and influential in 1844. Think that a living Nathan Hale might have had an influence on American attitudes towards England in 1844? That’s an analogy for Greece today.
More on Manolis Glezos:
https://infogalactic.com/info/Manolis_Glezos
I personally yield to no one in my love for the USA, and I have no doubt whatsoever that the US foreign policy establishment was trying the best they could to help Greece, and the rest of the region, for the long term. Still, it’s undeniable that some aspects of US, and US-supported, policy have been suboptimal regarding Greece.