"Pants" is short for "Hot Pants", gift horse.

The tip-off, I suggest, is the "Ah" in "Ah pants" which can be traced to "the Godfather of Soul"*, James Brown:

Ah hot pants won't make ya dance
But as slick as you are, ah!
You make the pants, uh!

from "Hot Pants"
Written by - J. Brown & F. Wesley

http://snipurl.com/fvtj

* 'Godfather of Soul' honored with bronze statue
James Brown celebrates 72nd birthday in Georgia
Associated Press, May 13, 2005

http://www.msnbc.msn.com/id/7771924