Greg (who sent his full name and I'll revise this if he wants) emails:
I recently google searched "reaction GIF culture" just to see what would come up, and I found this post -- in which someone posts a GIF of a scene from Glee as a reaction to some inane comment about gender bias in Pokemon. Anyway, the curious thing about the GIF is that it doesn't really need to be a GIF -- in it, the girl has an expression of exasperation, but her face doesn't move, and the only things that do move are some figures in the background and immediate foreground. Someone called this a spandrel of reaction GIF culture, an analogy I'm not sure fits 100%, but is a pretty interesting concept - that of a totally useless reaction gif, seemingly only used to acknowledge that reaction GIFs are typically used in such situations.
I like the idea of a placeholder for a reaction GIF - am also not sure if spandrel is the right word -- but this example is a classic (if banal) reaction GIF with the straightforward meaning of "long skeptical stare" or "slow burn." For that to be effective you have to know it's happening over time. The GIF gives you a sense of the room (school lunchroom [?] where people are moving around); it's fairly economical as these things go. As for its uselessness (animation vs still), the cheerleader is making herself into an "anger icon" by freezing that way, so including all the background movement makes it a fairly sophisticated joke (as opposed to overkill). As for the Pokemon issue, reaction GIFs are usually "off topic."