What does Boxing Day have to do with boxing?
1520s, "crafty, cunning," from fox (n.) + -y (2). Of colors, stains, tints, etc. from 18c. Meaning "attractive" is 1895, American English slang. Related: Foxiness.
Attractive; stylish; sexually desirable: She was 22 years old, a real foxy little chick with auburn hair/ She must be one foxy lady (1895+ College students)