baboon butt noun the red, sore buttocks of someone riding as a passenger on a motorcyle US
For the doubters among you, there are pictures, one of which shows Brooke hanging on tight and grimacing, an expression described in the caption as “a serious sign of baboon butt” – the rawness that afflicts first-time chopper riders. — WashingtonPost, p. W5, 3 January 1988