If you don't exchange contacts with the guy from the party you get stuck afterwards. Both available options lead you back to the same page and since you don't get the option to do a booty call you can't progress at all.
Similar situations when you don't drink enough alcohol at the party or don't give your panties in the pub. The latter of which requires you to have a certain level of corruption, meaning that you can't just go back a few pages and make a different decision like with the other two examples
