They're short with you. When a Gemini does interact with you, they might be short or dismissive. They may not seem interested in what you're saying, and they may answer your questions with one-word responses.
They gossip about you. If a Gemini doesn't like you, they might start gossiping about you to their friends and family. They may spread rumors or negative information about you, or they may just say mean things about you behind your back.
They're two-faced. A Gemini who doesn't like you may act friendly to your face, but they'll talk badly about you behind your back. They may also say things to your face that they don't mean, just to get a reaction from you.
They're unreliable. When a Gemini doesn't like you, they might not be reliable. They may not show up for appointments, they may not follow through on their promises, or they may simply disappear without a word.