A back-up friend
a friend you only remember when all your cool friends are busy and you have no one else to hang with
You text them: 'Hey, wanna hang?' They reply: 'Sure!' Then you realize you're the only one showing up to the party.
They're the one who shows up to your birthday and eats all the cake, then leaves before anyone notices.
You invite them to the concert, but they sit in the back and complain about the sound.