If you are bumchums with someone it does not always mean you both take part in anal love making. It also means you are really good friends. Comes from the word bumming or to bum . If you bum something then you really like it. E.g "I'm really bumming this new track!!" So a bumchum is someone you get along with really well and really like.
Person 1: "Hey Bumchum!!"
Person 2: "Haha Hey!"
Person 1: "What you been up to?"
Person 2: "Nothing Much"
Person 1: "Wow I love that new top!"
Person 2: "Thanks I'm liking your new haircut!"
Person 1: "Wanna come over my house after school?"
Person 2: "Sure!"
Person 3: "Stop bumming each other!!"
Someone who you think is great and who thinks you're great too. Comes from the word bumming which does not always mean the act of Anal Love Making but liking a person a lot. E.g "You're ALWAYS bumming her!"
Chumbums are people you bum (in the context as above) and who bum you!!
Person 1:"Hey Chumbum"
Person 2:"Haha! Hey what you been up to?"
Person 1:"Nothing much!"
Person 2:"Wanna come over my house"
Person 3:"You two stop bumming eachother!!"