So, a uniformed Marine walks into a convenience store, and says to the clerk, "Pack of Marlboro Reds, in a box and some matches."
The clerk gives the Marine the once over and says, "Sorry, son, but you look a bit young to be buying smokes. You 21?"
That potential scenario, in a nutshell, is the most common argument against a small but nascent movement to increase the minimum age to buy cigarettes from 18 to 21.
You can fight in a war at age 18, and vote in elections, but you can't buy cigarettes until your 21st birthday?
In Mayor Michael Bloomberg's New York City and on Hawaii's Big Island, that's now the case. And Utah, one of four states that had already hiked the minimum sale age to 19, is also considering bumping it up to 21.
Three New York counties and three communities in Massachusetts have passed minimum sale ages of 19; and in 2005, Needham, Mass., became the first and until New York passed its regulation last week the only municipality to approve a "21 law."
Needham has reported that since 2005, it has seen a drop of more than 50 percent in its youth smoking rate.
The scattered push for 21 laws is being welcomed by anti-tobacco groups, which point to research that shows cigarette addiction typically takes hold during a person's late teens and early 20s.
But the embrace of such age hikes comes with a caveat: Don't let this new battlefront divert attention from proven anti-smoking efforts.
"While we're enthusiastic about the 21 laws, we don't want them to replace what we have in place already," says Danny McGoldrick, vice president for research at The Campaign for Tobacco-Free Kids. "It's not a substitute for things we know are effective increasing cigarette prices by raising taxes, funding evidence-based tobacco cessation programs, and passing smoke-free laws."
Nonsmoking advocates like McGoldrick call the combination of those efforts the winning trifecta.
Big Tobacco argues that increasing the minimum age would drive buyers across state lines, leading to a loss in tax revenue.
Both sides of the smoking issue are also more focused on another, much bigger battle pushing for federal regulation of the relatively new electronic cigarettes, battery-powered devices that heat a liquid nicotine solution and create vapor that users inhale.
The Food and Drug Administration has proposed regulating e-cigarettes as it does other tobacco products, which would subject them to the same age-based limits on sales and marketing as well as other restrictions that apply to traditional cigarettes.
Big Tobacco is arguing for a separate classification for the product, which is increasingly popular among young adults and seen as a growth industry for the diminished domestic tobacco sector. While that debate plays out (the White House is reviewing the FDA's proposal to regulate e-cigarettes), the 21 law effort, while limited, continues.
New Jersey state Sen. Richard Codey has been pushing for the increase in his state, and in Washington, D.C., city councilman Kenyan McDuffie has introduced legislation to raise the age to buy cigarettes in the nation's capital from 18 to 21.
"We have an obligation to stay on the leading edge of smoking prevention strategies here in the District," McDuffie said in a release. "By restricting tobacco sales to young people, we can prevent many of our youth from acquiring a terrible, deadly addiction. Research shows that delaying access to tobacco products is an effective means of long-term smoking prevention."