Waking up to see "You have rights!"
In the United States, the 18th anniversary of one's birth commerates their offical entrance into human society. Young adults at this age gain the right to procure cigarettes, blunts - non-packed, those are illegal, pornography, bank loans, and a voter registration card among other things. Also, at the chime of midnight, one is magically responsibile for their actions after spending 17 years with no fear of servere punishment for their indiscretions. As if that weren't enough, you also gain true rights against search and seizure and other evils minors have no true protection against.
In short, you become an adult and suddenly responsible for your actions.
Don't ask me, I didn't make this up... We Americans have some strange inventions, don't we?