When a guy goes to kiss a girl on her lips, and she turns her head, and he kisses her cheek instead. A clue at the most basic, primal level that the girl is not really into the guy, but which many if not most guys miss.
Stan chuckled to himself when he saw Brianna give her boyfriend the cheek. "I have a chance!" he thought to himself.
Erin had been inviting Jason over to her apartment for study sessions. Jason was smart enough to figure he would be getting nowhere after he got the cheek one day.