Because it sounded funny the first time I
Which was when it appeared on my refrigerator.
I got one of those "refrigerator poetry" kits and was just putting the words up on the 'fridge at random, when one day - there it was.
And when you say it in a certain way: "I Puppy" - like " I, [state your name]..." - it has a certain silliness that appeals to me.
Anyway, here's how it looks on the 'fridge:
And click here if you want to see the 'fridge in its natural habitat.