I had got this hot pink office chair from a thrift store because it was comfortable, in pretty good condition and only five bucks. The only problem was it was DIRTY (and there was one edge of the seat where the plastic broke off). So, inspired by the Generation T books on reconstructing t-shirts into something else I decided to make a slip cover from a t-shirt. I found a hot pink t-shirt that matched the office chair at another thrift store on sale for just fifty cents (it was an 1x in size...but I think a 2x would have been better so I would have had more leeway).
I cut off the bottom of the t-shirt into one inch strips for the ties. Cut one part of the t-shirt to the approximate shape of the back of the chair and another part to the approximate shape of the bottom of the chair. Then cut little slits about one inch apart and one inch in from the edge of the fabric. I then threaded the strips for the ties through the holes, slipped the fabric over the seat and back and cinched the ties and tied them into bows.
Because the t-shirt material stretches, it conforms to the back and seat very nicely. And because the hot pink t-shirt was so similar to the original fabric (except cleaner), it almost doesn't look that different now that it is slip covered. :)
I think a larger t-shirt and one with a fun design on it would have been even better, but this turned out pretty well...especially for a first try.