Winning or losing a set 6-0. The zero looks like a bagel, hence the name. Getting bageled is humiliating at any level. Bageling someone at a Grand Slam is a statement of absolute dominance. A double bagel (6-0, 6-0) is the most devastating scoreline in a two-set match. It happens more often than you'd think, even at the pro level.
"First set, 6-0. She just got bageled by the world number one. That was 22 minutes of tennis."