There is no reasonable excuse for this, you're a horrible person if you advocate causing unnecessary physical pain to another human being.
However, for an ordinary skirmish, the chances of encountering someone who may be offended (and unable to overlook it) as a result of personal history is much higher than someone at a WW2 enactment, I would imagine.
But does one need to legitimise their offence before their objection holds validity, in many cases yes, but here - no.
I'll defend a lot of free expression, but bearing the nazi version of the swastika I cannot.
IMO this is offensive (doesn't make it not funny):
https://www.google.co.uk/search?site=&tbm=isch&source=hp&biw=900&bih=858&q=grammar+nazi&oq=gramm&gs_l=img.1.0.0l10.1072.2425.0.4463.5.5.0.0.0.0.82.298.5.5.0.ckpsrh...0...1.1.64.img..0.5.294.HAxS32Ilm7w&gws_rd=cr&ei=94W2VZD6I4Xue8jjluAO#tbm=isch&q=grammar+nazi+logo