Culo de Yak

Spanish slang for jackass as in jack's ass .

As a foot note:
In the words Yak the animal and Jack as in the name Jackson both 'J' and 'Y' are often pronounced the same way by mexicans especially those working at Jack in the Box (guelcome to yak in dee box, mine name ees paco) so purely by coincidence the use of a Culo de Yak takes in a charming double meaning

mexican1
"chimichanga tu madre "

mexican2
"tu eres un culo de yak !"

mexican1
"tu madre es un culo de yak!"