Third wheel，in english ：One who deters the socialization of a couple, perhaps when being invited out of pitty or through a feeling of duty. The third wheel may feel uncomfortable about watching the couple canoodle on his her her sofa,
1. Well, if your bring your girlfriend, I'll have to take my cousin with me, cause I don't wanna be the third wheel.
2. I'm not going to the movies with you guys tonight, I don't want to be a third wheel. It is like watching a poorly scripted romance movie!