Which of the following is an example of groupthink?

A good example could be:

A group of teenagers are hanging out on a Tuesday night. One person suggests going to a concert late at night. A few other members of the group think also think it would be fun. The one or two members of the group who don't want to go, are reserved, and go along anyway. Although the two members want to go on Friday night instead, they don't want conflict, and so, the other members think that they want to go too.

Groupthink will cause this group to make a possibly bad decision, and the two members to be unhappy.