when you decided to dance with that tramp instead of your girlfriend, that's when you decided to show your ass.
The further an unsuitable person is promoted, the more obvious his inadequacies become. In various more or less polite forms.
The filthe of her foli aperith more, as the filthe of the hynd partis of an ape aperith more, whanne he stieth climbs on high.
- c 1395 Wyclif Bible (1850) Proverbs iii. 35 (gloss)
He doth like the ape that the higher he clymbes the more he shows his ars.
-c 1594 Bacon Promus 102
The higher you climb, the more you shew your A—.
-1743 Pope Dunciad iv. 157 (note)
The higher a monkey climbs, the more he shows of his tail. - various