Pay attention to your nonverbal actions. Trust your instincts. If you think something is wrong, you're probably right. Get out of the situation immediately. If you choose to drink or use other drugs, you surrender the ability to think and communicate clearly.
Some people get themselves and their partners drunk in order to let sex just happen.
But consensual sex doesn't just happen. Consensual sex requires sober, verbal communication that is free of threats. Oregon state law recognizes that someone who is drunk is unable to give consent. Furthermore, being drunk is never an excuse for raping someone. Alcohol and sex can be as dangerous as drinking and driving.