Martinis are fattening?

I'm trying to identify this black and white film: A pretty young woman (teen-ager?) prepares martinis in her home's "bar" area for a male guest; he's several years her senior, and asks her "Does your mother let you drink martinis?" - to which she replies, "Yes - but she says I can only have 2 - She says they are fattening!" Not a lot to go on, but if you know, you know! Thanks in advance.