mug trainer
n.— «From the stable of newcomers Russell and Robyn Rogers who own the Rodmor Stud in Waikato and call themselves “mug trainers,” Veloz did not race at 2 or 3.» —“Racing: NSW hoop scores at Ellerslie” New Zealand Herald (Auckland) Sept. 30, 2007. (source: Double-Tongued Dictionary)
Further reading
It may not be as rich a source of slang as baseball, but golf has contributed several terms to English, including stymie, “to get in the way of,” mulligan, a “do-over,” and par for the course, meaning “normal.”...
Funny cat videos and cute online photos inspire equally adorable slang terms we use to talk about them. • Also, when a salamander is not a salamander, the story of an Italian term for a dish towel used halfway across the world, Bozo buttons...