Yes, there has to be a reason. Of course, it's very easy for an officer to say "He was weaving in traffic", or claiming you were speeding when you were not, or

Yes, there has to be a reason. Of course, it's very easy for an officer to say "He was weaving in traffic", or claiming you were speeding when you were not, or simply lie about you using a turn signal. I'll bet most people have a story like that. Probably from when they were younger, but not necessarily. And that's not even getting into "driving while black" and the likes.