my friend (and only nerdfighter friend IRL that i know of) recently got together for a Very Potter Sequel Watching Party, and decided we'd make some DFTBA shirts as well.
mine was an old black one i'd had forever, and hers was a white one she'd just bought. so, i got some masking tape, and we taped the letters onto the shirts. then we used a spray bottle and acrylic paints (not fabric paints, just acrylic. they work the same anyways haha) and splattered some on with brushes. then we let them dry (while we watched AVPS :D) and peeled off the tape and Voila!
i think they turned out pretty epic. i've been wearing mine all day!