Myself and three college buddies did an "around the US tour" one summer in a car. One of us knew a couple of guys in San Diego. We, of course, asked about Tijuana. They told us a horror story about returning to the US thru customs. Four guys in a car were on the way back and the border guards ask if you're a US citizen and they want to hear everybody answer. No passport required back then. One of the guys answered "Si, Senor". He was obviously a WASP, but they pulled the car over to an inspection area, and proceeded to take everything apart that wasn't welded. Then said, "OK. You guys can go." But the car was left in pieces. It took the four of them plus some other buddies with tools two days to put it back together.
The moral: Don't make jokes with the border patrol. They take their job seriously.