When there is a tight group of friends consisting of 2 guys and 2 girls who would probably end up having a foursome. Differing from the Fantastic 4 because there are 2 girls instead of 1, and 2 guys instead of 3. Standard foursome rules apply:
1: Guys can't make eye contact
2: Guys can't make bodily contact
*Exception*: High fives are acceptable
Person 1: "They're always together, I bet they're a Fantastic Fourgy"
Person 2: "We should form our own Fantastic Fourgy, and fight crime and stuff"