Normally heard in the context of `mutually assured destruction`; when something is mutually assured, it is guaranteed to happen to both parties involved. This phrase is normally linked to discussions involving nuclear weapons, where `mutually assured destruction` means that we are all guaranteed to die.

someone who is sexy beyond mean

An agreement between two groups of people that one thing or outcome is guaranteed to happen or be true.

When both parties are simultaneously guaranteed satisfaction.

Collective agreement. More than one thing acting together to ensure something happening

for a group of people to each assure each other of wanting to obtain something/someone