This is what you make when a friend in your group who has no other friends and no one even likes asks you to hang out with them and you do so out of pity. However, he/she is only tolerable if everyone else in your group comes over at the same time so the person gets placed in the background. This is reminiscent of a children's story of the same name in which something inedible (stone soup) becomes tolerable if everyone chips in.
"Susan asked me to hang out with her on Friday night. Can you and Matt come over so I don't have to put up with her alone?"