-Having any odd number of wheels on an object generally messes it up.
-Third wheel on a bike makes a tricycle, something thats safe for kids be left alone with.
Third wheelers make the situation extremely awkward for a couple to show affection towards each other or talk about things pertaining to their relationship.
Third wheelers also invade time with potential couples. Usually they are invited to hang out because of pity and consideration. It is also awkward for the one who unintentionally becomes the third wheel when the couple sort of distances themselves from them so that they can do things as a couple.
2 Guys & 1 Girl = Usually 1 too many guys
2 Gay Guys & 1 Girl = Should never happen EVER
2 Girls & 1 Guy = 99% chance theres 1 too many guys, BUT THERES STILL A 1% chance of this turning into the best night of his life!