To undo it we'll need to guess what you did. So just a few questions to narrow things down:
Is it just app icons that do this, or all screen touches? If just apps, is that only on the desktop, in the app drawer, or both?
Have you installed an app called a "launcher" or not? A launcher is an app which provides the desktops and app drawer, so if this is only happening with app icons it might be something to do with the launcher. In that case knowing which one you are using may help us (if you've not installed one then you have the default HTC launcher).
Do you have a menu in your settings called "Developer Options"? By default you should not (you have to do a bit of messing about to enable it), but if you have there are some funny things in there and conceivably it's one of them. If this menu is enabled don't mess with stuff in there, just let us know whether it's there or not.
Edit: I just had a play with my developer options, and none of them produced the effect you describe (a number produce strange visual effects, but none produced that effect). I have a different phone, but doubt those options are extremely different.