What is the general rule for showing just one card?

[youtalkfunny]

The general rule: No, you don't have to show it.

But many cardrooms are changing this rule, including one I played in the other night. This is not a change I agree with.

In fact, any "house rule" that varies from commonly accepted practice is a very bad idea, no matter how well intentioned. All it does is create confusion among the players and the dealers.