☛ Ross Zietz photostream on Flickr: “Life is Like a Box of Terrible Analogies” (slogan by Lawrence Pernica). © 2011 Ross Zietz

…and if somebody asks “What’s a bad analogy?,” one can always answer “A bad analogy is like…”.
Ross Zietz is a designer and an art director at Threadless. From what I understand, Lawrence Pernica (a member of the Threadless community) came up with the slogan and Zietz designed the shirt (he was inspired by Whitman’s Sampler boxes of chocolates). Image first spotted via This Isn’t Happiness.
There would be much to say about analogies (from Aristotle to Jacques Bouveresse). When using them, I wish I could (I try to) keep in mind two things: 1) How does it works (how do I think my analogy works, how should it works for others)?; and 2) What’s its value (the value I’m giving it and the value it receives from others: poetic, demonstrative, heuristic, etc.)?
In his Novum Organum (1620) Francis Bacon calls for caution when working with similarities and resemblances:

The human understanding is of its own nature prone to suppose the existence of more order and regularity in the world than it finds. And though there be many things in nature which are singular and unmatched, yet it devises for them parallels and conjugates and relatives which do not exist. Hence the fiction that all celestial bodies move in perfect circles, spirals and dragons being (except in name) utterly rejected. Hence too the element of fire with its orb is brought in, to make up the square with the other three which the sense perceives. Hence also the ratio of density of the so-called elements is arbitrarily fixed at ten to one. And so on of other dreams. And these fancies affect not dogmas only, but simple notions also. (Book One, § XLV; the Novum Organum was originally written in Latin, this English translation by James Spedding, Robert Leslie Ellis, and Douglas Denon Heath in The Works (Vol. VIII), published in Boston by Taggard and Thompson in 1863)