A Jehovah's Witness: 'flatnose' is a medical condition caused by spending a lifetime of having front doors slammed in your face by annoyed householders.
"Don't answer the doorbell Jane, it'll be that pair of flatnoses I just saw knocking next door"
Any music that is offensively loud with an excessive boom to it. Most generally played in a lac or Lincoln Clowncar rollin' roun' town wid a boomin system.