What do you find to be the most annoying conventions in physics? The classic example is the choice (darn you, Ben Franklin) of sign for the charge of the electron. Franklin had a 50/50 chance, and we ended up with the often confusing situation that current flow and particle flow are oppositely directed, that "up" on energy level diagrams corresponds to more negative voltages, etc. [EDIT: I think my earlier statements here about UPS conventions stem from a particular paper that isn't representative; never mind.... ]. Do any of you out there have other examples of really bad/misleading conventions?