1. Describing a person that barely has enough brain capacity to function in society by virtue of poor upbringing and their own stupidity.
2. Describing a person with an IQ around 70.
3. Describes a person that is severely brain damaged due to heavy drug use, yet still manages barely function enough to get by.
That fat kid is borderline retarded. If he was any dumber he would need to wear a helmet.
If your IQ were any lower we would have to enroll you in remedial classes because you're borderline retarded.
That borderline retarded stoner that works at the convenience store smoked himself stupid.