The idea that one man would feel insecure about another man's penis size suggests that he is using penis length as a proxy for sexual ability. This is only done by men as a way to try to show off to other men (based on the mistaken premise that it means something about their ability to attract women). It's useless to think this way because a big penis is not a turn-on to women, it can pound the woman's cervix and hurt, and it can be too wide to comfortably fit when having sex, and hurt. Women say all the time that it's not the equipment, it's what you do with it, and men ignore this all the time in misguided competition with men to see who has the biggest. Women don't go for the size of a penis, they go for the man and how great he is.
If what is really going on is that you are bothered by your daughter having a boyfriend and presumably a sex life, or you being in some way ignored or left by the wayside as she moves on with her life, then it might be time to talk to a counselor about those things. If what is going on is that you feel like a sexual rival to the boyfriend, please definitely talk to a counselor.
Why do you even know this?
Dude, what kind of question is that? First, don't be jealous of anyone else's penis. Second, why, WHY would the size of your daughter's boyfriend's penis be known to you? And why would you compare your penis to his in relation to your daughter? I am hoping that your penis size has NOTHING to do with your daughter. And her boyfriend's penis size has nothing to do with you. And really, between father and daughter with her boyfriend, you should keep your penis information to yourselves.