A fictional product invented by Homer Simpson on The Simpsons to cheer himself up. It is not sold at the Kwik-E-Mart, as Apu indicates, but it is seen in the background at the 33-cent store in a future episode. The name is probably a take on Meister Brau.
Skittle Brau consists of beer with candy floating in it. If it is not available pre-mixed, the requisite ingredients are a six-pack and a couple of bags of Skittles.
And now, the official quote from episode 5F03, "Bart Star":
Homer: I'm feeling kinda low, Apu. Got any of that beer that has candy floating in it? You know, Skittle Brau?
Apu: Such a product does not exist, sir. I think you must have dreamed it.
Homer: Oh. Then just give me a six pack and a couple of bags of Skittles.
Update 10/15/03: The Crazy Engineer has tried a few beers and alcopops with Skittles. Some taste nasty; others are more potable. Read the Skittlebrauology findings at http://crazyengineer.net/projects/skittle.php .