Rebecca Hains said the Transportation Security Administration agent at McCarran International Airport took her cupcake last Wednesday, telling her its frosting was enough like a gel to violate TSA restrictions on allowing liquids and gels onto flights to prevent them from being used as explosives. “I just thought this was terrible logic,” Hains said. Hains, who lives in Peabody, just north of Boston, said the agent didn’t seem concerned that the cupcake could actually be explosive, just that it fit some bureaucratic definition about what was prohibited.