I think it's very normal. It's part of the process of forming your own self-image about your dick. It's like looking at a guy that workouts all of the time. You see him and say to yourself, "I'd like to have arms like his" or "His biceps are wayyy bigger than mine" or "How can I get my chest to stick out like that?" Those thoughts are what gives you your
rank of yourself in your head.
You can do it with anything. A haircut, their style of dress, their body language and definitely a dick. It's the one thing that a lot of men are self conscious about and how no idea about it until someone tells you, "You've got a nice dick." You can
think all day long that you've got a nice dick or not know what to think about your dick and that's where the looking at other men comes from. You're working through your process to learn about yourself more.
Somewhere on Earth is a boardroom full of professional men and I would assumed that they're all wondering who's got the biggest dick in the room. If they had the chance they would all check each other out. So find comfort in knowing that you're not the only one that does it. I do all of the time