If you have the IHKA (automatic climate control) you can go into iDrive and change the settings to keep the system OFF.
As others mentioned...the design of an auto climate system is to be on...if nothing else to run the cain air through the microfilters to help with pollen/dust/etc. If you don't have allergies (yet)...this feature is MUCH appreciated when spores/tree pollen etc season rolls around.
In many BMW models with IHKA...the system will maintain whatever setting for around 16 minutes. So if you had the system OFF...then stopped at the drug store or bank etc...and you came back to the car within the consumer cut-off interval (which is usually 15-16 minutes)...the IHKA will remain OFF. If you return after a longer period like 30 minutes or an hour...then the IHKA will turn itself back on (usually at the lowest setting). If you still want the system OFF...then all it takes is usually a single press of the fan speed button (on the older gen BMWs...it was a single press of the
"-" fan speed button).
The FUNKY smell from the vents can be avoided by drying things out prior to putting the car away wet. The "smell" is created when you park the car in a dark & wet/humid enviroment (like pulling into a dark garage when you come home for the day). Bacteria & mold grow rapidly in a dark/humid environment.
So if you are parking (especially indoors) in the dark after running the AC...depending on what part of the country you're in or how hot it is...you can either shut down the AC (snowflake button) and just allow fresh air to blow across the condenser (you may have to roll the window down if tolerable). If the ambient temperture is too hot or humid and there's no way you're turning off the AC before parking in the garage...then use the "park ventilation" feature that allows the IHKA to run the blower for up to 30 minutes after turning the engine off and removing the key. This will have the same affect of drying the condenser and preventing mold and bacteria from having a perfect scenario for "getting it on"...which is going to end with you having that FUNKY odor every time you turn the blower on.