I say that he liked to expose himself a bit. Like any teenager, he'd be curious and engage in risky behavior. Especially given how few friends he had in his century.
In the case of green that'd be kind of like cutting.
In the case of red K, of course he's getting high. No matter what the effect of red K I think we can assume it's not a normal feeling.
And again re: Krypto: "super-intelligence?" Only enough to be darkly amusing, apparently...But that's like any dog too.