Forum goers on NeoGaf (on two threads) and Reddit have reported a number of Nintendo Switch devices becoming bent after prolonged use on the Nintendo supplied TV dock. The cause for the bend hasn't been revealed, however, it is being suggested that it has to do with high temperatures warping the plastic.
It's unlikely that the dock itself is the culprit, the general idea is that the warping is being caused by thermal couplings or vents being blocked. One user claims that the Switch's metal frame does not allow it to bend and says that it's probably an issue "with the injection molded plastic outer body which gives the console an appearance of being "bent" when it's really just a small flaw in one spot."
Switch owners have been testing out whether their devices are bent by holding a ruler to them, as seen below:
The warping is not occurring across all Switch devices, which makes it a bit hard to track down. If your Switch is bent, your best bet is to call Nintendo.