Dip

Someone who is really out of it, might seem like they're high; never really knows what is going on...at all. Synonyms are a ditz or a dumb blonde.

Ex. I can never make plans with Ashley because she always forgets and can never get back to me on time; she is such a dip.
2. I tell Tyler the same joke once a month and he never gets it he's such a dip I can't believe he's a brunette.