I'm so not looking forward to it/I'm so not over you

This is a common idiom among teenagers and those in their early twenties. It may be Australian in origin but its meaning is pretty obvious i.e. I'm not at all looking forward to it/ I'm not at all over you. Is there a similar teenage idiom in Greek?

Theseus, if you remove the "so" from your examples, the meaning does not change. While "so" is used an an intensifier in English, I would say that this particular use is American.
As far as I know, there is no one word that can be used as a direct equivalent in Greek, rather you will have to use different intensifiers for different phrases, but lets see what the others think.

In Greek, you use your tone of voice. E.g. Κι έχω μια όρεξη να σε δω...!, as an equivalent for your first phrase, but said mockingly.

Δεν το περιμένω με τίποτα! / Δεν σ' έχω ξεπεράσει με τίποτα/με την καμία!/ούτε με σφαίρες!

One way of creating this emphasis would be by adding «μα καθόλου» after the negative sentence, e.g.

Έχω την αίσθηση ότι κάτι τέτοιο πολύ θα ευχαριστούσε τους γραφειοκράτες ... κι αυτό δεν το θέλω, μα καθόλου! (Internet example)

Normally this would be: «...κι αυτό δεν το θέλω καθόλου!»

...
«Μα καθόλου» can also be further intensified by «όμως», e.g. «δε σ' έχω ξεπεράσει, μα καθόλου όμως».

Other than that, when I hear «με την καμία» that Azimuthios wrote - a relatively recent variation on «με τίποτα» (no way) perhaps affected by «σε καμία περίπτωση» - that teenage "so not" springs to my mind, at least; I think they both convey the same sense of slightly bending the grammar norm to create that age group lingo.

The first time I heard "so not" in subtitling, a passing thought was the monstrous «Δεν μπορείς να φανταστείς πόσο δεν» but, with a blahblah index of 5,6+ (a ratio of 34/6, including spaces), it didn't stand a chance.