Don't fall out with a friend over this little thing.
Tips
memory
掰 originally means 'to break something open with both hands' (as in 掰开玉米). Pair it with 闹 ('make a fuss') and the image is clear: quarrel so badly the relationship snaps in two. CC-CEDICT tags this as (dialect) 'to have a falling-out'.
usage
Softer register than 撕破脸 — 闹掰 is a straightforward 'relationship ended' without the explicit dignity rupture. Commonly said about friends, business partners, or romantic couples.
