Ya I sometimes say "this is retarded" but it is rare and afterwards I make an internal note to say something else. There are certain words that acquire a very negative connotation and I have a family member who is mentally handicapped. He has to deal with being bullied and being called "retarded." So it makes me feel sick to think that I would let a word slip that brings so much pain to other people, even if when I say "this is retarded" I am really saying "this is stupid" or something like that. But on a deeper level it is wrong that I associate "retarded" with stupid, and that's the root of the problem. Even though my family member would get called "retarded" he is actually very kind, generous, helpful, and smart when you take the time to get to know him.
I"m in the same boat exactly. I have a cousin with Downs Syndrome and I think of him each time that word slips out of my mouth. I don't say it often but when I do I feel an immediate sense of embarrassment. The last time I remember saying it was on this day. I said it to mk and apologized. He admitted that once in a while he has similar slip ups. But I think I said it like 3 times that day. Was an emotional day.