A commond bond in both subjects having fucked the same vagina.

Two guys who have fucked the same chick.

If boyfriend dick is a dick you can settle down with. And vacation dick is a bit overwhelming. There needs to be a dick in the goldilocks zone. This is bigger than the boyfriend dick and you just want it all the time. Like how you long for your brother's love.

When you and your biological brother dick down a female together

Two dudes who have seen each other’s dicks and are used to it. Usually between two close dudes