mesmerized by penis size?

It's also often used as a synonym for hypnotize. I'm sure one could use a big dick as the focus object in hypnosis. There are certainly plenty of hypnosis stories where a big dick is what is used to put someone under. And I'm sure you could find people willing to see if its possible!
 
Yes, it's quite easy too.

Just pull your dick out, swing it back and forth very slowly and repeat the words... "Yooou are getttting verrrry horrny" over and over. When you see the persons eyes get all swirly looking you know you've done it.
 
Mesmerized is when a guy walks into a wall while catching a peek at a gal's boobs. One time a lecherous manager where I worked did exactly that when he tried to get an eyeful of my boss' secretary. When he hit the wall, Karen jumped up and with great concern asked "Mr. Bernsen; are you OK; what happened?" It was all I could do to keep a straight face.
 
yeah I was 2 days ago at the gym. saw a guy in the locker room, smallish guy, around my age, not a great body but he had one of the hugest cocks Id ever seen. Was obviously strolling around enjoying the attention. I really did feel mesmerized, cuz I just followed him into the shower and showered next to him. It was hard to tear my eyes off his cock. He slowly got hard, but pretended not to notice me staring as we both soaped up. Finally, he looked at me and smiled and right away leaned over and put his arms around me and kissed me on the mouth. Then he started licking my pecs. It was weird cuz I wasn't so much into him -- I felt a little uncomfortable being kissed naked in the YMCA showers -- but I was truly mesmerized by his cock, and his cock only.
He later tried to entice me to a more private place in the locker room, but I just ignored him and dressed and left.