A Texan, we'll call him Duane, comes into some money and decides he'll go back and fulfill his teenage goal of attending college. He meets with the dean of the local college, who signs him up for classes in engineering, math, and logic.
Duane says, "Logic? What the hell's that?"
The dean says, "Let me demonstrate. Do you own a weed-whacker?"
Duane says, "Yep."
The dean says, "From that I deduce you have a lawn, and a fairly decent-sized lawn."
Duane says, "I do!"
The dean says, "That also tells me you own your house."
Duane says, "I do!"
The dean says, "And you are about thirty years of age. Since you own a house, I deduce that you have a family."
Duane says, "That's right!"
The dean says, "I suggest further that you have a wife, and you are heterosexual."
Duane says, "I do! And I am!!"
Later, Duane meets up with his friend Shane at a bar. He excitedly tells him about his day on campus, and the wonderful world of logic.
Shane says, "What the hell is logic?"
Duane says, "Let me demonstrate. Do you own a weed-whacker?"
Shane says, "Nope."
Duane says, "Then you're gay."