For all of you offended by 'retarded'

All those words are acceptable; it's all in the context of the situation. I wouldn't ever say alright retard, spaz or spastic to someone with a disability. They wouldn't like it, neither would I use it so openly to describe someone with a disability. It's widely used as a derogatory term, therefore the instant connection with certain descriptive words is offence. However, I would say them to my friends in jest.

For example, let's say the context of this situation is a group of people at work talking and I say
"I saw this retard yesterday falling over". It's not cool.

If I was writing a report for some kind of academic or business document and let's say I worked in social care:
The baby is showing signs of neurological damage and signs indicate the infant maybe retarded.

The latter is better than the former. The former could offend someone. The fact is there are better choice words that can be used that don't offend people; if you're actively seeking out words and causing confrontation then I would suggest opening your vocabulary and being a bit more creative.

What works for one bunch of people doesn't work for others. I think it's important to respect boundaries and not push too much. If you want to say retard a whole bunch of times, do it away from people who are offended then you won't be pissy about them being offended, they won't be offended; everyone wins.