Who said "I can't help it. That's just how I am."?

This quote is attributed to Snoopy.

I can't help it. That's just how I am. - Snoopy

"I can't help it. That's just how I am."

Snoopy

"I think I'm dying. Send for a doctor immediately!"

"Rats! Another day, another disappointment."

"Sometimes I lie awake at night and ask, 'Is life a multiple choice test or an essay?' Then a dog barks and I realize it doesn't matter."

"I love mankind. It's people I can't stand."