An exaggeration of 'cankle'. Whereas 'cankle' is a contraction of 'calf-ankle', 'thankle' is 'thigh-ankle'. Indicates that there isn't just no discernable ankle, but no knee either.
Speaker 1. Sally has such cankles.
Speaker 2. No, they're not just cankles, they're THANKLES!
12 step recovery jargon referring to someone new who talks about how great life is, now that they'resober. Usually meaning that the person is out of touch with reality.
The new guy seems pretty happy for a dude who has no job, no money and no family. He must be on a pink cloud.