My brother is so lazy.

This joke gets its chuckle from a delightful blend of absurdity and irony, playing on our expectations of a common cultural item: the bumper sticker. Usually, these adhesive messages are meant to communicate something specific about the driver's personality, interests, or even a warning, like "I brake for animals" or "I brake for yard sales." The humor here comes from subverting that expectation entirely. Instead of a meaningful or even quirky message, the brother's sticker proclaims a complete lack of purpose in a driving action, which is inherently nonsensical.

The real-world context of bumper stickers is key to why this works. They’ve been around for decades, evolving from simple advertisements to personal declarations, often reflecting a driver's political views, hobbies, or even just a funny quip. The idea of someone being so incredibly lazy that their car's warning system reflects that lack of effort or reason is a hilarious exaggeration. It takes the stereotype of extreme laziness and applies it to an unexpected, public display, making the punchline both surprising and perfectly fitting for the "lazy brother" setup.