If Doug's cholesterol is so high, it's likely that he is taking cholesterol medication. If that is the case, he would not be eating a grapefruit for breakfast. Grapefruit and cholesterol medication do not interact well, often causing severe kidney damage and can even be fatal. Being a "Doctor" (Dentist) he most certainly would know that.
After Bobby squirts ketchup on the bald biker's face it cuts to another angle and there is also mustard. It then switches back to another angle and the mustard is gone. The mustard on the other biker's face also changes between shots.
In the scene where they are riding on the highway and they get splattered by bugs, Woody gets hit by a bird after overtaking Bobby and Dudley. While he is struggling with the bird, he clearly overtakes Dudley and then Bobby. Then the next shot, Bobby and Dudley are behind Woody and Doug.
In one shot you see something being thrown through the window and breaking it. In the next shot, when Dudley comes in to confront the Del Fuegos in Maggie's diner, the glass behind the biker sitting at the right of the screen is fixed again.
As the Wild Hogs first enter Maggie's, Maggie is seated at the counter. However in the very next shot she is standing behind the counter with her back to them. In the same series of shots, she also turns her head to look at the Wild Hogs twice.
Throughout this movie, the characters' wristwatches were clearly visible in many shots. In the bull-slapping scene, which took all of ten minutes in the movie, the times on the men's watches were all different and changed dramatically in each shot.
At the end of the movie, when the Wild Hogs arrive in California they are seen driving south on Highway 1 in Malibu. A few shots later, they are seen driving north on Highway 1 between Venice and Santa Monica beaches at the conclusion of their trip.
After they supposedly leave Ohio and before they get to the sign that says "Welcome to Missouri", they cross a long bridge over a very deep canyon. That had to be filmed out west, there are no canyons that deep between Ohio and the Missouri state line.
When the Hogs are gathering on the road in "Cincinnati" in the opening scene, the background has architecture and landscape not widely seen in Cincinnati - ranch homes, tile roofs, trees down the median and straight split-lane neighborhood streets, flat terrain (Cincinnati is hilly), blue-painted metal lamp posts inner-city, and horizontally-mounted traffic signals.
Doug calls Kelly late in the day on Sunday, any by early to mid Monday morning, Kelly and Karen arrive in what appears to be the family minivan. It would take over 20 hours to drive from Cincinnati to Madrid at 70 MPH without stops.
After Woody retrieves Dudley's bike and they are riding past the del fuegos you see everyone (Wild Hogs) waving with their left hand. However, Woody sends a hand signal using his right hand - the one needed for the throttle, yet you hear his engine speed up.
In the scene where Peter Fonda's character asks the Wild Hogs what do they call themselves, the F symbol on Fonda's jacket is on the right side and he is looking to his left, the next time we see him, the F symbol is on his left side, reversed, and he is looking towards his right. It is obvious the film negative for the scene is reversed.