Will a reverse lens ring ruin your camera?

The Reverse ring macro results are fantastic as compared to buying expensive macro lenses.
There is always a risk of the lens being exposed to dust - its better advised to use this technique in a controlled (studio) environment.
Using a reversed lens outside would be risky as it could damage it beyond repair.
Also, keep in mind that, you require ample amount of light to click shots since you cannot adjust the aperture settings while using this technique.
Lastly, the Depth of field is very, very shallow and you might have to take several shots of the subject to get a couple of good results.
Hope that helps :) (My setup - Canon EOS550D / Reverse Ring / Canon50mm1.8 / Softbox + Speedlite Flash EX430)

Hi, If by reversing you mean, taking of the lens and attaching it reversely to the camera, first the lens wont fit of course, and yes there is still a chance of taking a picture, but careful, cause the camera hole will be exposed to dust and something can enter on so sensitive zone.
But you can get pretty images.