[Mithrandir]

In a 6 handed game the other night with all 6 people still in, I went all in before the flop. I had a king/deuece of clubs. 2 People called.
The flop was 2 clubs and an irrelevant card. The other 2 people checked.
The turn was a King, both checked again.
The river was a 3rd club on the board. One person bet, the other folded.
So I said what do you have? The guy who bet said, I've got Kings. I then said I've got Kings... I then momentarily paused and said, but I've also got a deuce of clubs. Showing the King high club flush.
The guy who lost the hand then got mad because I didn't "call" the flush immediately. And because I "called" that I had a pair of Kings he thought we should split the pot and that he shouldn't have lost.
I was always under the impression that the cards speak for themselves.
Granted, it could be viewed partly as a **** move on my part for not saying I had the flush right away. However, you can't exactly ignore the cards. I mean, in a casino a dealer is having you place your cards on the table and then the best hand showing wins.

Keep in mind this is a friendly game and I was just busting his balls a little.

Has anyone ever seen this as a house rule people use? I've always been under the impression that the cards speak for themselves. One of our friends said: "Well then why don't you just call a royal flush all the time."
And what if someone mistakes their hand? You can't ignore the cards.

Any feedback is great. Thanks.