It's supposed to be used jokingly (please dont killpeople..it's not nice)
It's explained in its self.. not much else I can say.
You've been my b.f.u.i.k.y for almost 5 years, and although you can piss me off occasionally, your the coolest person I've ever met and I love you bro, you're not LIKE my sister, you ARE my sister..
T.Y.D.S.I.M.W.M.H.B.B.I.U.I is from the famous song Washing Machine Heart by Mitski, For example the lyrics βToss your dirty shoes in my Washing Machine Heart. Baby, Bang it up inside.β