So, I had a silly thought about this one little detail in “Clerks”. When Caitlin is talking to Dante, Silent Bob comes in and buys something. I, personally, could not make out the label, but I remember reading that it was a pack of icing sugar. Chances are, it was just an off the wall thing for Bob to buy, but I sat and built a theory around it.
Right before Caitlin’s arrival, Dante had an unpleasant interaction with Rick Derris. Rick is Jay’s older brother. While we’ve observed that Jay’s relationship with Sylvan Derris is stable, if not exactly warm, we don’t really know anything about how he and Rick get on. Being Rick’s brother obviously doesn’t do Jay any favours, as he is refused to ride one of his company’s buses in “Strike Back”. No little brother perks for Jay.
Considering we know that Rick is pretty shallow, and a bully, we can assume that Jay was probably quite the punching bag, as a kid. This would definitely explain a lot about his prickly and defensive attitude as an adult. And this is pushing it a bit, but it wouldn’t surprise me if Rick was the type to let the matter of different fathers come between them. It evidently doesn’t matter too much to Sylvan, but I bet Rick gave Jay a really hard time about it, growing up. This would have made Jay much lonelier than he would have had to be, had the siblings all stuck by each other. This is also probably why Jay never gives his surname, only his first. He does not feel any close connection with his known family.
With this in mind, we don’t see any interaction at all between Jay and Rick in “Clerks”. Chances are, it just wasn’t relevant to the story, or perhaps the idea of them being siblings was not yet in place. But, again, we’re going on a theory/headcanon. I think that either Jay and Rick had a pretty nasty interaction, or Jay actively avoided even facing him. After whatever it was, Jay was upset, so Silent Bob wanted to cheer him up.
We’ve seen Jay eat pure sugar, before, in “Chasing Amy” when he’s pouring spoonfuls out of the cellar. I think that he wanted something sweet, after seeing Rick, and decided only icing sugar would do. So, that’s what Bob got him. Then, in spite of the fact that Bob seemed very tired that day (I’ve said, before, that I think he just wasn’t masking that day, due to fatigue. Hence, no special gestures, or expressions that he normally uses), they dance together. Maybe that was to cheer Jay up, too.