I'd like to say every day, but I know jeans always go 3 or 4. But they rotate. So its not 3 or 4 straight- its 3 or 4 before wash, with other jeans in between.

You can change your pants?

Nope. I have enough jeans and dress pants and button down shirts to last a couple weeks without washing. However, I am in my 30s and have 9-5 job working as a hydrogeologist (bachelor in geology and masters in hydrogeology). So it is kind of expected that I wear clean clothes everyday and that they are in good condition. And I get paid enough to do that. :)

When I spill that sweet chocolate inside those chocolate chip cookies all over my pants I ussually decide its time to change them... and that probably happens everyday ;P

I think to accurately answer this I need to know how old you are.  I'm 27, and so I change my pants everyday, and sometimes more than once a day.  If you are in your teens though, every few days as long as you're changing your underwear everyday.  Don't wear underwear more than once unless you are desperate.  And rotating pants might be a good idea, no problem if you dont wash them after every wear, but wearing something for days in a row can make it smelly, let those pants breath a little.  

Personally I like to wear fresh clothes everyday, I feel clean and, more importantly, the ladies notice if you wear the same clothes multiple times.  As I like to play the field, I need to stay fresh.  

Nah, the ladies do notice sometimes if they are crazy, a girl that has that much time noticing your clothes isn't interested in you in any way, maybe in your clothes, or your looks, but not you.

Also, to my real answer to your question, It's all about how dirty/smelly the trousers are, but jeans are ussualy fine a longer time than other trousers, which means if you don't stain heavily they can even last up to two weeks without getting a personal stench, just keep your shirts and undies clean and all should be fine ;P - the major reason why I can't and don't change that often is because I can not afford enough pants to change them often, I have 4 pair of jeans that are suitable to go outside (the rest is (partially) torn appart or eternaly stained with acryl-colours) and I can only use the shared cleaning-room of my house every two weeks without using it in the time between 2 am and 6 am (which my neighbors would really dislike).

Like I said earlier, just change your undies and shirts everyday and you should be fine.

Thanks guys, now I feel normal.

uhm usually unitl it's getting dirty (mud for example) or it starts getting smelly (which takes a loooong time)
So I usually wear the same pair of jeans 3 weeks in a row. However when I'm at home I always wear shorts.

Every single day! WTF?