- If you've never taken a psychedelic before, you don't know how you'll handle it. 2c-b is pretty forgiving, as far as psychedelics go, but it could still take you for a ride. You might become anxious, paranoid, have a bad trip, who knows.
- While I have nothing against taking psychedelics for fun (they can be a blast), you might be missing a chance to have unique experience that goes beyond partying. Especially for your first psychedelic experience, I would personally want to wade in from a calm environment and allow your mind to take you where it will, rather than having the party dictate.
If you're not an anxious person, there's a good chance that 18mg of 2c-b, as your first psychedelic, at a house party, could be a lot of fun. But, it might not be, and more to the point, you might miss out on a good portion of what psychedelics are all about.
Anyway, just make sure you are super-comfortable with the people around you. IMO that's the most important thing if you are going to do it.