The smell of weed/ alcohol or you just acting in a strange way is probable cause. How ever thats where is gets sticky, headed to the wrong side of town, or head light out or speeding is not probable cause. Acting like a douche bag or even kinda acting in a way that is inconsistent with how a jury would act in your situation is probable cause. How ever you can deny them the search it doesn't matter how hard they want to bully you or be an ass you can simply say no ( even if they have probable cause [ unless your on probation or parol]). That being said if they ask you to step out of the car roll all your windows up and step out and close and lock the door behind you ( this doesn't mean you are guilty you are simply securing your belongings). If you say no to a search they will have to get a warrant ( they wont be able to get a warrant to search just because you said no) but be advised you will end up probably getting some form or fashion of ticket. Try it next time you get pulled over and they want to search your car say no, they will ask you to step out of the vehicle and when you do make sure all your windows are up and when you get out lock your door and close it behind you. Your vehicle is secured at this point in time and they will have to have a search warrant, the catch to all this is if they can see something from a window or they call a K-9 in and the dog alerts to something. But at this point in time if they have smelled weed in your car your playing a pretty shitty game and truth be told you have a 25% chance of the dog actually showing up ( most counties only have 1-2 on at a time unless your in a larger one and they have 4-5) but even if they are waiting on a dog to get there and they have you detained they can only do it for so long before you ask the wonderful question of are you charging me with something or am I free to go? And at this point in time you have put them into a situation that most of them don't want to be in because if you are waiting on a dog you have a good long while to wait most of the time ( this is called False imprisonment). This has all come from an Sheriffs Deputy I work with on a daily basis BTW.