Chelsea and Charlie discuss Alan's loneliness and Chelsea decides she's going to set Alan up on a blind date.
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Charlie talks to Alan after he sleeps with Rose to try and talk some sense in the poor bastard.
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Alan gets a little lonely and ends up being obsessed with building model cars, such as the Scooby Doo mystery wagon.
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Charlie helps catch Berta up on all the events that happened the the previous day... such as Rose and Alan going on a double date with him and Chelsea. Wait... what?
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Two and a Half Men Season 6 Episode 21 Quotes

Chelsea [about Rose]: Fun personality right?
Alan: Unfortunately she six more of them

Alan [getting ready for double date]: How do I look?
Charlie: Don't open that can of worms, you are what you are