Yes, there have been numerous opportunities for me to compare. And I hope there will be many more.
When the OP ask about comparing I understand that means assessing the size of some other guy’s erection when you are in generally close proximity to them. And comparing doesn’t necessarily mean you are going around taking actual measurements. It is a real time event you view and make mental notes about.
If you have lived to be at least forty years old and are gay, straight, or anywhere in-between, it is hard to imagine that you have not seen (and mentally compared with) a number of live erections. If this does not describe your life experience, I would suggest you have (are) failing the challenge of male socialization. And I don’t think I am being overly critical.
Please ask yourself how you have been able to avoid participating in a meaningful way with half of the world’s population. From grade school forward most males have been tightly associated with other males. They were your intimate friends who spend the night, or went camping/fishing with you. You play sports together under the most intimate of conditions. They are your cousins, your neighborhood gang. You served in the military together, put them to bed when they drank too much, shower with them, shit with them, and sleep in a bed next to them for weeks at a time.
Unless you are blind, you know what hand your buddy uses to brush his teeth with, if he eats with his mouth open, and most likely what his farts sound like. Erections are normal, frequent, and just something you learn to expect when you live around a group of other males. They are a constant topic of discussion, a source of great humor and pride, and a unique area for male bonding.
If this has not been a part of you life experience, then you have missed a great deal. In a larger picture, this should prompt you to assess the kinds of experiences you do engage in and the empathy you bring to share when socializing with other males.
Bottom line is you are just a male like all the rest of us. Every other guy in the world knows what you have, how it works and how it makes you feel. So lets celebrate what we have in common and move on to more important matters like learning how to get along.