Is this a Simpsons quote?
 

This morning the line "Carpe canem...seize the dog?" popped into my head. I think it may be from The Simpsons, but I'm not sure. Can anyone help me out with this?

I don't think that quote is Simpson's specific even if it was used on there. There are tons of websites out there with "latin seizers" like that.

Well, I remember this sequence happening in some cartoon:

Person A gives advice to Person B. Person A means to say "carpe diem" (seize the day), but they say "carpe canem" (seize the dog). Person B, suddenly motivated, walks outside, sees a dog, and picks it up. Puzzled, they say "Carpe canem...seize the dog? This doesn't seem right." Still, they continue on, holding the dog.

I'm thinking The Simpsons, but it may have been a different cartoon.

I tried a web search, but like you say, I only found the lists of "latin seizers".

Oh wait, maybe it's The Critic...any ideas?

Okay, never mind, I did a search, and the thing I was thinking of was in fact "The Critic".

yeah - i was just about to say that it was the critic - great show - ended too soon - there were running new shorter eps at shockwave.com for some time but that seems to be done now

A variation of this was used on Buffy.

Willow tells Buffy 'Carpe Diem' to which a puzzled Buffy replys: 'Fish of the day?"