1. Deprive yourself of sleep as it will weaken your immune system.
2. Like someone else said, get cold or be in a wet and moldly environment as it will also weaken your immune system.
3. Overexert yourself. Will also weaken your immune system. For example, shouting, screaming, or anything with voice and over doing it could help increase your chances to gain sore throat which could help with acquiring strep throat.
4. Like someone else said, eat expired food.
5. I recomend you don't do this but if you want to get Salmonella, eat raw meat. (SERIOUSLY DON"T DO THIS)
6. Be near sick people.
7. Don't wash your hands.
8. Be dirty and have poor hygiene (except for your teeth, always brush your teeth!)
9. Use old and wet toothbrushes since they will have bacteria.
10. I don't know...eat dirt or lick the floor or something.
Why am I encouraging this?....
Feel free to check my school thread to discuss your problems. What's wrong with your school? Don't you learn something new everyday?