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1.
A situation where a brother and sister are engaged in a session of 69. At some point (sometimes unintentionally) both parties braces become entangled in the other party's pubic hair, leaving each member no choice but to forcefully detach each member's pubic hair while still entangled in their braces. hence; the name lawn mower. (see:Cincinnati Wool Teeth)

Named after Cincinnati, the location of the first documented case.
Mother: Brian now you and your sister have braces at the same time! How cute!
Friend: Yeah Fitz! How Cute!

Brian: Yeah, whats even cuter is the Cincinnati Lawn Mower we had after the orthodontist appointment.
by luckiePee-air November 04, 2009