The dinner check arrives and, what do you know? Some people have to use the restroom.

Meanwhile, others pick up the bill with a grin. They, too, may be scheming.

Nearly 30 percent of young people offer to pick up the tab because they're in pursuit of credit card miles and perks, according to a new survey from CreditCards.com, which interviewed 1,005 adults in the beginning of May.

Some 13 percent of baby boomers do the same.

"Those moves are how people really ramp up their rewards," said Matt Schulz, senior industry analyst at CreditCards.com.