How about "four-flushed flounder"? No? Too insulting, I suppose.

Equivalent to lunkhead? Hm.

Bait-breath?
Ocean dweller?
Poor excuse for Poseidon? or
Poseidon wanna be? (or could use Neptune in either)
Reason for tartar sauce?
King of Atlantis (uttered in a sarcastic tone).

Any help? Or muddied the waters further?

mmouse

Time is too slow for those who wait, too swift for those who fear, too long for those who grieve, too short for those who rejoice, but for those who love - time is eternity --Henry van Dyke