One of the selling points of the USB-C plug is that there is probably no way to insert it incorrectly. As [Pim de Groot] show with a ‘Cursed USB-C 2.0 device‘, the reality is a bit more complicated when it comes to USB 2.0 compatibility in USB-C. He made a PCB that elegantly demonstrates the simplicity of the problem with two LEDs. Only one direction of the USB-C connector causes one of the LEDs to burn green, and the other direction causes both LEDs to flash red.
The reason for this behavior is simple: if [Pim] explains, although the USB-C plug only has a single pair of data lines (D +/-) for USB 2.0 connection, the receptor duplicates it on either side of its pins, protruding two pairs of D +/- lines. Normally you will connect the corresponding lines in these pairs to ensure consistent behavior regardless of the plug orientation, but you do not have to do this.
By routing each USB 2.0 data pair to its own SAMD11C MCU, only one of the MCUs will be connected to the USB, causing the connected MCU to cut the LEDs. With a little more circuits, it is possible to detect in which direction the plug is placed and use this information in a single MCU system, which changes the behavior. While at first glance it is little more than a fun party trick, it also provides insight into a possible failure mode of USB-C 2.0 devices where only one proportions work, due to broken tracks or cushions.
(Caption image: Cursed USB-C 2.0 device, by Pim de Groot)