Money is truthful. If a man speaks of his honor, make him pay cash.
Lazarus Long, engaging and flawed protagonist of Robert Heinlein's "Future History" series (Orphans of The Sky, Time Enough For Love) kept a notebook filled with delightfully blunt aphorisms about life, death, women, power, and other important things of the here and now.
Never try to outstubborn a cat.
Lazarus is immortal and has lived through many generations of humanity. It's this perspective which allows him to cut to the chase with such incisive wit time and time again - when he says, "You live and learn, or you don't live long," you get the feeling he has seen both sides of this hypothesis proven repeatedly. Occasionally, of course, his observations are quite caustic - that was Heinlein's style, abrasive, unflinching - but the entire notebook is tempered with a Steven Wright-esque "never thought about it that way" style. Complaints about Heinlein's misogyny and general negavitity aside, the book is just downright funny.
When a place gets crowded enough to require ID's, social collapse is not far away.
First published as the teaser interludes to the 1973 novel Time Enough For Love, demand eventually forced a publication of the Notebooks as a separate book in 1978 through G. P. Putnam. The first edition had lovely illustrations of the aphorisms by D. F. Vassallo, and as a coffee table book, it is best left open at all times to my favorite quote from it,
Everybody lies about sex.
Surprisingly, you can find almost all of the quotes online (though not in one central organized place), but I highly recommend that you get a hardcover edition (one is put out by Pomegranate Books on occasion) and pass it around to give your friends an insight into the unique and penetrating mind of Lazarus Long.
Heinlein, Robert. The Notebooks of Lazarus Long. Pomegranate Books:Los Angeles. 1991 ed.