When you unintentionally become a third wheel with a friend and their boyfriend/girlfriend. It is unintentional because no one likes being a third wheel. For Example: A friend will invite you to hang out with him/her but will not tell you that their boyfriend/girlfriend will also be joining you, so then you get there and you are a third wheel. Usually caused by a friend not telling you that their boyfriend/girlfriend will be joining you at an event or hangout, because they are inconsiderate towards how you will feel being the third wheel.
commonly makes the person who is third wheel'd angry but they cant say anything at the time of the incident because you don't want to make a scene in front of your friend's girlfriend/boyfriend. mostly argued about with friend who third wheel'd you the next day.
Man 1: Yo, i totally got third wheel'd last night! It was so annoying.
Man 2: What does that mean?
Man 1: When Jimmy invited me to hang out at his house last night he didn't tell me that Ashley would be there too. So then i became the third wheel and had to sit there while they snuggled and made out.
Man 2: That sucks. Jimmy's a dick sometimes.
Don: James what the fuck! why did you fucking do that last night?
James: do what?
Don: you fucking third wheel'd me last night! you invite me to your house to play xbox and instead you have amanda there and i was the third wheel and it was awkward as hell!
James: oops my bad.