I particularly hate the confusion that BSP and NPT cause. They're almost interchangeable (differing, iirc, probably on the angle of flank) and will get about three turns in and then leak or fail under pressure. In my world, this has led to graduate students spraying liquid nitrogen around. It's clearly the case that the two probably were supposed to be identical but diverted due to manufacturing differences in the distant past.

The standard advice I've been given when it comes to either vacuum or cryo fittings is "cut anything American off it as soon as it arrives and put DIN standard or KF kit on as soon as possible". Standards are a pain and that xkcd about there being too many of them is very, very true.