R.M. stands for retarded midget or in rare cases Retarded Mini-Person. This type of little person has not only been stricken by dwarfism but is also mentally retarded. They can be found in fast food resturants, as janitors, and in supervised R.M. groups. In the instance an R.M. is spotted, the person should make no loud noises or sudden movements, as the R.M. may attack out of instinct.
"Holy shit! On my way home from work I stopped at Wendy's and a R.M. was working the pay window. Luckily I avoided eye contact and slowly removed my food from it's tiny little grasp. I'm just happy I made it out alive."