Final answer:
Frieda's behavior at the concert can be best explained by the concept of Deindividuation, where she acted out of character due to the effects of being in a large, anonymous group.
Step-by-step explanation:
Frieda's unusual behavior at the rock concert is best understood in terms of Deindividuation. Deindividuation is a social psychological concept that highlights the impact of group situations on individual behavior. In these contexts, an individual may feel a sense of anonymity, leading to a reduction in accountability and a decreased sense of self, often resulting in behaviors that the individual would not typically engage in if they were alone or not in a large group. This concept applies to Frieda's situation, as being part of a huge crowd at a rock concert likely diminished her usual inhibitions and led to her behaving in a sexually provocative way, which is uncharacteristic of her typical shy demeanor.