Your character would only think what you would think.
You don’t hear anyone else’s thoughts when you’re talking to someone, right? (Most people don’t anyway.) You can guess what someone else is thinking from their expression, body language, words or tone. Many times, you can guess pretty accurately just from these visual and audible cues.
But you can’t really hear your friend thinking his thoughts. Neither should your character.
Judy thinks Alvin is pompous and full of himself. She can’t hear his thoughts, so she wouldn’t know Alvin thinks Judy is irresponsible and flighty.
Mary thinks, Charles just doesn’t understand me. She wouldn’t know Charles is thinking, I think I’m finally starting to understand her. So your reader shouldn’t be told this, either.
However, your character can speculate on what the other character is thinking.
Judy can tell by Alvin’s expression that he thinks she’s a dumb blonde.
Mary can tell Charles thinks he’s starting to make headway, but he doesn’t know he’s completely missing the point.
When you’re writing the scene from your character’s point of view, stay in that character’s head—don’t go wandering into someone else’s thoughts!