This is a hoot. From the WaPo:
A joke President Bush told recently in Montana struck several readers as very familiar when it was recounted in yesterday's Style section. In Bush's telling, the joke involved a city slicker asking for directions in Livingston and being told to look for two 'cattle guards.' Now, everyone in cowboy country knows a cattle guard is a metal grate that keeps livestock from straying. But this fellow is so clueless, he asks: 'Hey, what color uniforms do those cattle guards have on?'
But in 1978, when Dubya was running for Congress in Texas, the very same joke was on him.
Nicholas D. Kristof has the details, in a New York Times story from 2000, describing that 1978 congressional race:
"A candidate forum was under way, and his rival was needling Mr. Bush with an oft-repeated joke in which he was the punchline, a yarn that reinforced a perception of him as a spoiled rich kid from back East. Kent Hance, the Democratic candidate and a smooth-talking good old boy, was telling a yarn about working in a field along a rural road. Then along came a fancy car. 'It was a Mercedes,' drawled Mr. Hance, raising his eyebrows, and the audience tittered knowingly at the hint that Mr. Bush was the kind of man more comfortable in a Mercedes than a pick-up. 'The guy rolled down the window and wanted to know how to get to a certain ranch.' Mr. Hance recounted how he'd given the man directions, telling him to turn right after a cattle guard, a metal grate ubiuitous in rural roads to keep livestock from straying. 'Then,' Mr. Hance continued, 'he said, "what color uniform will that cattle guard be wearing?"' The audience roared with laughter, and just to be sure that the voters got the connection with the Connecticut-born Mr. Bush, Mr. Hance said he had noticed something else about the Mercedes: 'It had Connecticut license plates.'"
Bush lost that race.