Geninne D. Zlatkis has no trouble stitching on t-shirts. Look at this lovely work! Geninne is an artist living in central Mexico who works primarily in watercolors. She's embellishing with thread one of her own works transferred as an iron-on onto a very soft, dark t-shirt. You can follow her progress (and see her other work) here on Geninne's Art Blog. (I follow DoorSixteen on Twitter, who tweeted the link to Geninne's work.)
Let me guess: you want to stitch on a t-shirt now, right? People are forever asking me about stitching on t-shirts (often as a first embroidery project) which is one of the trickiest, most fruuusstrating and swearing-inducing fabrics you can attempt to embroider. Why? Because it's a knit, not a weave. You know those finger cuffs that only get tighter the harder you try to pull your fingers out? The same thing is happening when you are trying to pull needle and floss through a knit. It just won't let you escape. (Fortunately, cousin Joey who suckered you isn't there laughing at you.)
Lucky for you! Yesterday, I just re-posted my How-To: Dark or Stretchy Fabrics Part 2 that tells you how to tackle t-shirts, and dark and stretchy fabrics.