I would like to know how to thin the consistency in regular store bought icing? I know I won't always have time to do icing from scratch...

Then make some ahead of time and keep it in the freezer. Seriously. The canned crap doesn't come close to homemade buttercream.

Absolutely. Make a huge batch and freeze it as needed. Canned frosting is not only awful, it's more expensive than scratch and it doesn't crust. And I used to like the stuff-- until I started making my own.

In a pinch i use canned chocolate frosting. to thin it just ad a LITTLE water or milk until you get the consitancy you want. To thicken it ad powder sugar.