text: Don't get angry or upset with them.  Instead, if they whine TO you, say something like, "I prefer not to speak badly about my employer and colleages."  Say it in a totally neutral tone of voice and then go back to what you were doing.  At first they might be a little bit angry, but that's just because they've suddenly realized that their behavior is not appropriate.  If it happens repeatedly and/or in front of customers, I suggest speaking to your supervisor about the potential negative effects this could have on business.  Alternately, get your mom or dad to anonymously write a "Comment Card" saying that they don't want to shop in that store because the high-school age employees make them uncomfortable with all their whining!