(akin to Bad Hair Day); When a gal's normally perkybreasts don't seem so fresh or vital on a given day.
Poor Carol - at the pub after work on Friday, her always luscious boobs were, as usual, the center of attention and much commented upon (privately), even through her blouse and pantsuit. And now here it is the following Monday afternoon: she's had to skip lunch because of an emergency meeting, she's missed an important deadline, a fight or two with a client and alas, her normally shapely knockers seem so much the less today - slightly frumpy, a tad saggy and OMG ! have they SHRUNK ? She's evidently in the midst of a bad boob(s) day.
when you are walking on a higher level than a girl (eg; when she is sitting down or you look out from a freeway overpass) and she is wearing a dress and you can see her naked boobs from your angle.
"Hey! Check it out! Look at that chick below the bridge!"
"Wow! We've got a bird's eye boob!"