Is “that’s so retarded” really actually quite offensive?

In high school, I regularly used “that’s so retarded” and “that’s so gay” to mean more or less the same thing, although “retarded” usually implied “unnecessarily and baroquely stupid; obtuse” where as “gay” usually meant “unnecessarily and wastefully (in the utility sense) restrictive; ‘lame’ .”

I stopped using “that’s so gay” after I met gay friends that found it offensive. I now find it offensive. I stopped using “that’s so retarded” after a friend of mine who has an autistic brother was offended by it. I recently started using it again (although far more sparingly than I did when I would rifle off off-handed put-downs in my high school days).

There’s really no good substitute for “that’s so retarded!” It may just be the case that one can either be successfully descriptive at the cost of being deemed an asshole; or one can be inoffensive at the cost of a succinct and, at times, perfectly apropos phrase (or indeed a number of them, as the slope slides).

Cheryl and I talked about this at some length when I made the more or less conscious decision to reinstitute “retarded” in my vocabulary. Certainly, I mean no offense by it. I wish, in fact, that there were some totally different word that could be used to replace the literal meaning/etymological origin of the, I argue, entirely new and different word “retarded” that I use, which is actually simply a homophonic homograph

It’s not the image of the mentally retarded that I’m going for. It’s onomatopoeia mostly. Cheryl offered “That’s so ridiculous” but it doesn’t do the same thing.

It may be indefensible. I mostly want access to what I think is ultimately an incredibly poetic phrase, without offending people. To that end, my current plan is to only use it around people who I can be sure will interpret it to mean what I want it to mean, and not interpret it to mean what I don’t want it to mean. I’m not sure if that’s having my cake and eating it too, or if it’s only eating cake when I’m not around people watching their weight.

Any pointers? Am I just an asshole?