'Tis a day dedicated to booting people up the jacksie i.e kicking them up the arse. Popular with school children. Also you should note that it can be any day the kicker chooses and they can kick you in the shin if they so wish.
Kid: *runs up and kicks you in the shin*
Kid: Jack boot day. HA HA!
Kid *runs off*
You: WTF?? *hobble home*
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