It takes place during one of the first few weeks of summer after school gets out. You and your friends try and do as many things for the first time as you can
Example 1

Friend #1: Dudeee, I just smoked weed for the first time
Friend #2: Happy #FirstWeek my friend

Example 2

Friend #1: Wanna go get drunk?
Friend #2: In the spirit of #FirstWeek, hell yeah I do
by OrangeTheMarker June 30, 2013
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