My favorite is: We're first. Assuming we make it out of the solar system and so on, then just imagine the practical jokes we get to play on future civilizations

My favorite is: We're first. Assuming we make it out of the solar system and so on, then just imagine the practical jokes we get to play on future civilizations: Whoopee cushions crafted out of gas giants, mysterious "ruins" that have no bloody purpose at all, ancient stone tablets that end with "Assuming a spherical cow in a vacuum..." Some archeologist, 20 millions years hence: "Oh god, not /these/ forerunners again." It wouldn't be all bad, being first.