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Crikey! What a clamour of responses! Though as expected, it's pretty inconclusive, but gravitates towards "doesn't matter either way".
Interesting that weecalf has raised the issue of being chided for being left-handed, and I've sometimes wondered whether my mother's childhood experience of that may have fed through genetically into me in the womb: She was forced at school, as a left-hander, to write with her right hand, and was chastised for using her left hand. The result of this was that she became very confused over the years as to which side was which, and her writing was never neat or straight.
I like the analogies with opening packs of crisps at the wrong end, etc, which I've done many times, called myself a berk, then continued to eat them regardless. But if a packet of biscuits contains on its wrapper the words "Open by cutting", I absolutely refuse, and will defiantly and laboriously loosen the welded corners of film at the end until I have a nice neat tunnel which I can fold back down when I've extracted adequate biscuity supplies. Or if a packet says "Open other end", again, I will absolutely not comply. Mostly one finds it makes not one whit of difference.
And 'milk or tea first?' doesn't bother me at all - I've always drunk my coffee black, as I think milk spoils the taste of coffee, and it also leaves a scummy film on the mug, thus necessitating washing it after every drink - which you don't have to do with black coffee (or tea) for at least a month!!