To n73 is to have a momentary brain malfunction whilst high. Letting ones brain wonder away from the situation and the speaking aloud the thought train.
Term comes from when a Nokia n73 locks up for a moment and shows nothing but garbage on screen until it unlocks moments later and is working just fine.
For e.g. If the subject is traveling in Nathan and Carolyn's car towards Nathan and Carolyn's house then the subject says "So when are we going to meet up with Nathan and Carolyn?"
Dude you totally just n73ed