What sort of a rug was it?

Berber rugs are usually negatively charged. Plastic (polyester) rugs are usually positively charged. Rubberized rugs (like a doormat) have no charge at all because they are insulated.

The other question deals with the type and color of shoe. A leather soled show usually is a negative charge if the show is black. A brown show may be different. A rubber soled shoe, again, will not have a charge.

Basically, @ziah too many variables.