To be energetic in a happy and friendly way. Also used to describe relatively small, friendly, enthusiastic mammary glands found in the human female. E.g.: "She has nice perky breasts". Past a certain age, male interest in "perky" breasts takes on a shabby flavor of dirty-old-manism; when the day comes that your daughter's got 'em, you'd best have grown out of it. Really.

Perk"y (?), a.

Perk; pert; jaunty; trim.

There amid perky larches and pines. Tennyson.

© Webster 1913.