Hmm, I'll pick some of my favorites from two languages, plus my favorite French phrase: English - reciprocate, schizophrenia, encyclopedia French - pamplemousse (grapefruit), qu'est-ce que c'est que ça? (what is that?)
Antidisestablishmentarianism was always good for frustrating people who wanted to copy everything I said. I also like sanguinivorous or sanguinovore, because that's what I wish I was.