America's 1st Legal Weed Purchaser -- I'm Not Smoking It!

The first man to make a legal weed purchase in the United States ... ever ... is doing the most un-stoner thing possible with his new stash -- he's locking it away in a safe.

32-year-old Sean Azzariti tells TMZ, he's storing his 3.5 grams of Bubba Kush, his truffle edible, and his $57 receipt from the Denver dispensary where he bought all the stuff because he plans to donate it to a museum.

"It's a piece of history, dude," Sean says.

But Sean didn't go un-high on the big day -- he tells us he blazed through some weed from his personal collection to celebrate the momentous occasion, and subsequently binged on gingerbread waffles with apple puree.