It’s a time-honored tactic for challenger brands of all types. They puff out their chests and spit in the eye of their strongest competitor. Often they put products side by side in public and claim superiority. Other times it can be more subtle, where the competition is un-named, but understood by all. I’m talking about the high-risk, high-reward marketing gambit of comparative claims, used most often by bootstrap brands to lift their perceptions and their sales, they hope at the expense of their rival’s bottom line.

The most dynamic comparative campaign of all time is undoubtedly the Pepsi Challenge that ultimately baited Coke into one of the biggest marketing blunders of all time. Pepsi’s comparative approach actually began in 1975 in supermarkets with head-to-head taste tests of the two colas. By 1985, as Pepsi was drawing even with Coke in supermarkets, though not in overall cola sales, Coca Cola caved and introduced the infamously ill-fated New Coke. Big Red was saved from its mistake by the intense brand loyalty of its customers, who demanded a return of the old soda formulation. Can you imagine the monstrous spike in social media sass and silliness had Coke made the same goof in this decade?

But while Coke vs. Pepsi was a subjective battle of taste buds, some challengers throw around serious fightin’ words. Pennington grass seed is one of many brands marketed by the California-based Central Garden & Pet Company. But Pennington has taken dead aim at lawn and garden behemoth Scotts, with a comparative program that challenges Scotts’ product quality and the brand’s integrity as well.

“We’re Pennington, the grass seed people and we’re proud to tell you the truth about our Pennington One-Step Complete,” is how two TV spots open. One goes on to explain that “their EZ-seed” (with a shot of the actual Scott’s package and brand by that name in a dusty corner of the shed) requires more watering. In a second spot running this year, they chide Scotts EZ-seed for being 50% filler, and show a crate full of sawdust as evidence. Both spots and much of their marketing conclude with the tagline, “Honest green.” That’s one hardball slogan. You’d think these brands were running for political office or head cheerleader.

“I can understand what they’re doing, right up to the point that they questioned our honesty with ‘Honest Green,’ and that sucks,” recently appointed Scotts Chief Marketing Officer Jim Lyski was quoted as saying in Ad Age. While “that sucks,” isn’t the PR response I would have recommended, Scott’s has also fired back with ads refuting the watering claim and pointing out that Pennington products contain ground-up paper as mulch. Ironically, there is some question about which is the challenger brand in this case. Scott’s is by far the bigger brand overall, but Pennington claims to be the leader in grass seed. So in effect Pennington is donning the cloak of the underdog and using it to build their grass seed brand. Clever marketing, indeed, but while challenging an established rival is one thing, calling them a liar can be distasteful to the customer. The Pennington brand is following a tricky path.

Apple was far more subtle with its long-running “Hi, I’m a Mac. And I’m a PC.” campaign. Their target was clearly computers with Microsoft operating systems, but it was conducted on a seemingly more friendly, unassuming basis, which is part of the nuance of the Apple brand in general. Apple’s comparisons elicited chuckles: Pennington’s are more of a gasp.

Lawsuits aside, comparative claims by challenger brands also carry the risk of actually helping the targeted brand gain awareness. This is why leading brands should be careful about inadvertently boosting a smaller competitor by naming them, or even by legitimizing another brand’s claims with a response. It’s possible also to be so good at being the challenger that the marketplace keeps you there. Avis and their “We’re #2, we try harder” campaign has never gotten them within sight of Hertz. Pepsi has fallen to third place in the cola wars. And while Apple is wildly successful as a technology company, the computer business is less than 20% of their revenue now and holds only a small piece of overall market share in that category.

Pennington has thrown down the gauntlet to Scotts, but all brands should be wary of the classic children’s retort regarding rubber and glue. And it can get just as messy with brands as it does on the playground. Honest.