What are the side effects of mixing cough medicine and alcohol? Especially if you use cough medicine to get high then drink to get drunk?

Misuse. Wow - this is a loaded one. Firstly - do not mess around with medication or chemicals to get a high - this is sick. Secondly - drinking to get drunk is a disease of addiction. Both practices are bad and means that treatment is needed. Never mix cough medicine with alcohol and never take one to get high and the other to get drunk.
Binge drinking? Mixing any med or other chemical substance with alcohol to get drunk is dangerous. Even if your peers do the same, it's high-risk and probably covering up underlying issues. Please see school psychologist, nurse or social worker to talk about what you're doing and ask for help. Often parents are the last to know what you're doing; but tell them if you can. See: https://secure02.kidshealth.org/teen/drug_alcohol/alcohol/binge_drink.html# I hope this helps. Please be safe.