when you catch them randomly making plans without you and not informing you. When they got their own inside jokes that they don't even bother explaining to you etc
When all three of you are walking, stop and pretend to tie your shoes. If no one notices, then you're not a part of the duo. Because the partner in the duo will always take notice
So uhhHHhh i think their is a duo in the trio im a part of so can someone give me the most OBVIOUS SIGN that im clearly being left out