Bad manners
From Hard Drop Tetris Wiki
In multiplayer games, to show bad manners or BM is to disrespect the opponent.
Common BM methods include:
- Spamming the hard drop key;
- Soft dropping every piece;
- Using impractical openers such as the Sus Opener;
- Taunting the opponent in chat.
As the term implies, it is generally considered rude to BM, especially in ranked or tournament matches where serious play is expected.