This one is clearly reserved for the reptilian, amphibian, and fishy pets, for whom cold-blooded isn't just a way to describe your ex, but also a physical condition. Any pet owner who's ever bought a heat lamp or a heating pad knows how little control geckos, snakes, turtles, frogs, toads, and fish have over their body's temperature.
Why? Because they're lazy, lazy, lazy ectotherms. You know, when I was kid, lizards would walk twenty miles in the snow everyday just to get a heat lamp, and the heat lamp would only be 20 watts, but they made due with what they had. Nowadays these spoiled brats expect us to wait on them hand and foot. "Um, excuse me, but I'd like the lamp to be 80 watts, not 40. Otherwise I get lethargic and my body processes slow down significantly and it's bad for my health and it's possible I could die." Well, lizard, maybe you should thought of that before you became cold blooded. The rest of us are warm blooded and it's pretty damn sweet.
(flickr photo Green Gecko by dominigs81; http://www.flickr.com/photos/dominiqs/1349256667/)