All this POV talk recently on here makes me wonder if something I recently tried is working. I think it's working, but maybe I'm still too close to the material. So, here's the deal. The latest short story I've finished is written in first person. I do not deviate from that at all. However, I sort of include what other characters are thinking, but it's what my MC thinks they're thinking. I think it's pretty clear given that everything is in first person, but instead of saying, "I think he thinks I'm a loser," I would just say, "He thinks I'm a loser." Does that make sense? The situation my characters are in is one that is predictable for them so my MC already knows what others are going to say and think to some degree. I don't think I'm breaking any writing rules with this. It was more a way of streaming the prose. I've done this throughout the story. Again, I think it works, but I'm second guessing myself a little. Maybe it's just because it's a little different than the way I usually write a story. I was going through it again today. Obviously, it's not a switch to third at any point. My example is a good one to show what I mean. Any thoughts? I would love to hear them.
You're fine. The speculative nature of reading somebody else's thoughts is always implied. Unless they're capable of actual mind reading.
As long as you make sure we know that this is a thought of your viewpoint character (with quotation marks, or italics for thoughts, or something), then it's completely consistent with the first person perspective. In fact, I think it's a pretty good addition to the first person perspective, since us humans are prone to worrying about what others think of us, so it adds another degree of realism I don't recall noticing in works I've read before. Bravo!