Sounds like a blatant angle shoot, at least as you described it. In particular, there's no rule that says that your hand is dead because you showed it (unless you plainly tossed it face up into the muck, I believe -- EDIT: I'll defer to the previous post because I don't play many B&M tournaments; still, it doesn't apply HU).
In general rules should be interpreted against the best interest of the angle shooter (at least IMO good floors believe this), hence it's a call.
The preceding poster is correct, though -- you should wait for a clear verbal declaration before showing your hand.
If you want something more definitive, feel free to consult
Robert's Rules -- the preceding is just my educated guess.