She likes to smoke it upppppp.. just like me! (:
420 = 4/20 = April 20 = National Weed Day
420 mean weed ect. so my guess is that's what she is talking about.
She smokes weed.
420 is said to be the international time to smoke pot. It has been said to have originated from police code for a marijuana bust but this is untrue. Some say that waiting until 4:20pm to smoke marijuana enhances your appreciation for the 'treat' :) Outdoor growers typically plant their outdoor crop on or around April 20th (4/20), which is said to be 'Stoners New Year.'
So 420 friendly means that she may not actually use marijuana, but she is ok with marjuana and its underlying culture.
"Clarity is defined as a state in which one fins them self when they go too long without good marijuana"
It is not a sexual thing, though I can understand the mistake. It means she is ok with marijuana and those that smoke it. It is not a reference like 69 or various others.
It is reference to a web site called my420friends.com which is a web site around pot smoking. It probably means that you are pot smoker friendly or you smoke etc.
I would assume its something to do with Marijuana use. Either to say that she uses or that its alright for you to use.
However when in doubt ask her. She should be more than willing to tell you.