I'm trying to remember a joke that goes something like this:

What is the difference between a ___ and a ___.  The ___ is
interested, the ___ is commited.

I believe the joke you're looking for is this one:

What is the difference between involved and committed?
In a bacon and egg breakfast, the chicken was involved, the pig was committed.

Hope this is it! Feel free to rate this answer or ask for clarification. :)

Either that's a strange joke or I lack a sense of humor.

could it possibly be :
What is the difference between a Man and a Woman.  The Man is
interested, the Woman is commited... or maybe the other way around? 

but with this keyword I found alot of similar jokes , you may enjoy
them even if they are not what you are searching for:

://www.google.com/search?q=%22What+is+the+difference+between+a+%22+interested+committed+joke&hl=en&lr=&start=10&sa=N

~Angel1

Definitely the bacon and eggs, the chicken was involved, the pig
committed. I laughed the first time I heard it but it seems rather
bland now.

the version of this i heard had the question "what's the difference
between a chicken and a pig at breakfast?"

it's a little snappier.  but then again it's more of a riddle than a
joke.

i actually heard this in the context of of some kind of activism, like
the peace corps or mothers against drunk driving or something.  it's a
little more relevant there.