Using dish washing liquid on your auto paint will strip off any of the good "stuff" which is on there, such as waxes and or oils. This leaves it unprotected. If you use stuff specifically for washing your car, you'll leave the wax in place and it will last much longer between applications.
This site says it pretty well:
While the detergents in dish soap do a great job cleaning the car ... they also remove much more than just the dirt from the surface. The detergents break down the wax, stripping it away and leaving your paint dull and unprotected.
Good car wash soap will not contain any detergents and will be rich in lubricants (which safely lubricate the dirt, allowing it to glide from the vehicles paint). A “feel test” you can use to test your car wash is to put a small amount of it between your finger and thumb and rub it back and forth. You will notice that better car washes will be much more slippery. Lesser ones may contain detergents to “help” clean the car (since the lubricants aren’t there), so make sure you check that before buying.
EDIT: To answer your real question, though, it won't ruin your paint work, but will leave it dull and lifeless. You will have to rewax every time if you expect it to look good and stay protected. I'm not sure why you'd want to do this when you can just use car wash instead and not have to worry about the wax every time you wash your vehicle?