In an effort to find something positive about this episode, I have to say that...ummm...the Impala was very shiny.
Also, Sam was adorable giving that little dog the best belly rub ever.
Sorry, I'm afraid the cheap laugh school of humor just isn't my thing. There were more genuinely funny bits in the "then" segment than in the episode itself. Pretty much the only part I found genuinely funny was Dean's plan to kill Chef Leo: "Empty one of these in his head, see what that does."
The whole episode kind of reminded me of one of those Saturday Night Live sketches where they take a one-liner's worth of idea and beat it to death for five minutes. I get the feeling the writers just started with 'Dean takes on dog traits' and then labored ineffectually to build an entire episode around it.
Hopefully, next week's ep will be better.