It really irks me when people swap "i.e." and "e.g." - i.e. stands for id est - "that is", and indicates that exactly the items listed, and no others, are meant by the  phrase that is being clarified, while e.g. stands for exempli gratia - "for the sake of example", and indicates that the listed items are only a small number of examples of a larger set, and that many items have been omitted.

When I read, my brain always tries to apply the corresponding meaning when I come across i.e. and e.g., and it breaks my brain when the wrong symbol was used, which I find very annoying.