So I'm going to a party this weekend with two girls who are good friends with each other (I have hooked up with one and the other said she would definitely hook up with me). The party is supposed to be a three-way birthday party for us and a mutual friend half-joking suggested that we have a threesome. He has now committed to making it happen as his birthday present to me. One of the girls said that "it would only happen if she was really drunk", which almost seems like an okay to go for it because there will be lots of alcohol at the party. The other girl just laughs when he brings it up but doesn't really object or agree with him. My question is how can I go through with this in a comfortable manner? I'll have no trouble with flirting with both of them, but I'm not sure how I'd go about actually initiating anything. Any tips or suggestions would be appreciated.