Explanation: Mostly just memeing - while Romans could be immensely prickly about why they chose to go to war, they placed a high value on ius bellum - 'justified war' - wherein some form of legal and moral reasoning was employed before choosing to go to war. They were often very meticulous in examining minutiae in search of offense to give themselves an excuse to go to war, mind you - but it was generally things that we would recognize as, if not justifying war, at least justifying offense.
At the same time, it must be recognized that when a Roman could not find an excuse for a war he wanted, he made one - provocation was perfectly legitimate, and the hypocrisy of it generally ignored. If the barbarians did not wish to cause offense, they should not have responded in such a predictable way!