I was given a very plain very boring grey dress made out of tshirt fabric on the w.e and I was wondering if anyone had an idea of something exciting I could with it??

Maybe gather parts of the skirt part up so it drapes and replace the sleeves with lace and you could turn the neck line into a square neck.

You could try doing something like this project
http://www.cutoutandkeep.net/projects/tshirt_rose_dress

If you know how to sew Yo-Yo's (typically used on quilts) you could cover it in that or in petal/scale shapes that overlap. I saw a dress like that once and it was amazing.
If all else fails there is always tie dye!