Officially An Adult?

I remember seeing a facebook friend post something about officially feeling like an adult on the day she received a poinsettia as a gift from a student.  It wasn't when she graduated college, got engaged, got a job, bought a house, moved in with her significant other, got married, or got pregnant, but rather, the moment when she received this gift that she officially felt like an adult. 

I had a similar moment when I voluntarily prepared brussels sprouts as part of a meal.  At the time I was 28, had been living alone for several years and was financially independent.  But yet, this random moment hit me.  

How about you?  What was your 'holy shit, I'm an adult' moment?  I firmly believe this is something that sneaks up on you - it's not in one profound moment (a college graduation, a first day of work, etc.), but rather, etched into the details of daily life.   What was your moment?