How to disarm and correctly dispose of tear gas spray?
Do not open, do not try to neutralize it yourself! Bring it to Recycling center (DE: Wertstoffhof). If your city is 100k+ there should be one. That's the place where you bringing your old furniture, the rubbish after renovations, and so on. They have a part for disposal of hazardous waste (DE: Sondermüll). What usually comes in there are paints, old car batteries, old pesticides, etc.... Another possibility - if you have some friend at chemistry school of some local university, give it him. Each Chemistry faculty has some "disposal" facility.