The more serious answer -- for opening boxes I'd use a box cutter. It can be adjusted so that just a "tooth" pokes out, preventing it from cutting the contents. As long as you use it just to open boxes (i.e., cut tape), it can be sharpened, which is what I do, actually.

A folder or a fixed blade is often too thick and too long, thus requiring a tad more skill & concentration to wield. (I know all of you guys are familiar with this issue, so just quiet down.) After a while slivers of tape get stuck to the blade, sometimes even making it harder to cut.