Saeviomagy said:
When you take a readied action, your action is resolved before that of your opponent, and your initiative is also before that of your opponent.
Since your opponent has not acted yet, he is still flat-footed when you get your go.
In a hyper-literal interpretation, "Freeze or I shoot" and "I ready my action for if he does anything" would have to be restated as "render yourself helpless or I shoot" and the readied action would be "I ready my action to shoot if he does anything except render himself helpless".
And it is perfectly possible to give up your dex bonus. I believe the optional rules on striking cover include the possibility (ie - if you want to give cover to a friend, you can choose to discard your dex bonus to allow a projectile to strike you). Although that may be 3.0...
Actually, you have two errors in what you wrote here:
1) I was answering his question about flat-footness, not about being denied a Dex bonus. These are two different game concepts:
"Flat-Footed: At the start of a battle, before you have had a chance to act (specifically, before your first regular turn in the initiative order), you are flat-footed. You can’t use your Dexterity bonus to AC (if any) while flat-footed."
2) When a readied action goes off, not only does the triggering action have to have a specific action that it triggers on ("I ready if he does anything" is discouraged in the DMG because it is not specific), it also does not occur before the initiative of the character who caused it. It interrupts that action, but that does NOT mean that it occurs before the character is no longer flat-footed.
For example, you ready an action to fire your missile at the first character through the doorway. My character walks up to the doorway and walks through. I did a move action BEFORE your ready action occurred. Your initiative in future rounds is before mine, but that does not mean that you acted before I got to act.
In the case of you readying an action to fire at me if "I do anything" on a surprise round, I can perform a delay action of my own which will not trigger your action:
"By choosing to delay, you take no action and then act normally on whatever initiative count you decide to act. When you delay, you voluntarily reduce your own initiative result for the rest of the combat."
You cannot stop this. You cannot deny me the ability to no longer be flat-footed.
Once I delay, I HAVE had a chance to act, hence, I am no longer flat-footed. Once I do anything, even though your Readied Action occurs before my action, I have had a chance to act and hence, I am no longer flat-footed.
According to RAW.