You misjudged your commute to the pub they have chosen to have this at (which, for whatever reason, is the exact compass inverse of where you live, talking proper two-buses-and-a-train sort of journey here), which means you show up an hour-and-a-half late – but despite that, none of the people you know who you assumed would be there already (and laying down a little rolling boil of a vibe to augment this current one, which is tepid at best; I mean, there is a baby here), so you are stuck here on your own, astray in a sea of anonymous people who all look mostly sober.
At some point in your mid-twenties, birthday celebrations clicked over from, "I’ll tell you what Spoons I’ll be on on the day, bring as many drugs as possible" to, "Have you met my friend, Sylvia? She’s 45 and plays the flute. For fun! For actual fun!" and you realise that the people around you are not your people: so many hardy, Borough Market-branded tote bags! So many shirts tucked into jeans! You offer a drink to someone and they put a single palm up to say no, because they drove here and they intend to drive back. Where are you? What is going on here? Someone baked a cake—