The mirror, funny and cool with the lines bit seems rather like he is actively trying to woo her.
When I wrote what I thought about that line, it was how I remembered it from just hearing the song in the past. I didn’t think it through intellectually* today. Now that you point this out, that is a bit suspicious. However, the insistence throughout the song that he wants a woman like Jesse’s girl is more important, I think, so my opinion stands.
*Did I really just use that word about a rather simple-minded pop song? 
The mirror is just him being insecure. The most he seems to be actively doing is being “funny” and “cool with the lines” and wishing this made her fall into his lap.
Would you give the singer this much benefit of the doubt if he was singing about Jophiel’s girl? Lol. When you’re in love with a beautiful woman, you gotta watch your friends.
I remember situations like this happening in high school. A couple of close friends meet a girl. Sparks fly and suddenly one of the guy’s is the third wheel watching these two date.
High school romances came and went frequently. Jesse’s Girl is a bit more intense because the romance may lead to marriage.
I don’t see the guy as hero or villain. He hasn’t done anything wrong yet.
Btw, this is similar to the plot of the Graduate with Dustin Hoffman seeing Katherine Ross getting married.
No, but then I’d be emotionally vested. Same reason why I probably shouldn’t serve on the jury of the guy suspected of stealing my car.
It’s also similar to the billions of times guys have been jealous of a woman in theatre, song and real life.
“Jesse’s girl” is a stand-in for any woman like Jesse’s girlfriend. Singer has been “cool with the lines” not to Jesse’s girlfriend but to other women like her and just hasn’t gotten anywhere. He wants to find a woman who is responsive to him but hasn’t yet been able.
Or he’s just trying to cut Jesse out of the picture.
The tragic point of the whole song is that Jessie’s girl is named Stacy and Jessie is really in love with Stacy’s mom. 'Cuz she’s got it going on, of course.
If Jessie would get off his butt and make the move to Stacy’s mom this would all sort out just fine for everyone with the exception of Stacy’s dad.
Glad to help,
Bubba
Seriously, though, he doesn’t even think of her by her name. Does he even know it? Does he care? Is she even a person to him?
From Is Rick Springfield's Jessie's Girl a Real Person?, based on Rick Springfield on Oprah Winfrey
Oprah asks Rick the question on everyone’s mind—is Jessie’s girl a real person? “Oh, yeah,” Rick says. “All my songs start from a core of a relationship.” Although his fantasy girl was real, Jessie wasn’t. “Her boyfriend’s name was actually Gary and not Jessie, but Gary just somehow didn’t sing right,” Rick says. “So I changed it to Jessie.”
Rick can’t say Gary’s girl’s name—because he can’t remember what it was! “I was never really introduced to her. It was always just, like, panting from afar,” he says. To this day, Rick thinks Gary’s girl doesn’t know the famous song is all about her. “As far as I know, she doesn’t know,” he says. “And I lost contact with them before the song came out.”
So, if it was “panting from afar”, he’s not doing anything. I see the “charade” in the song is him not getting involved - staying afar.
And I think the looking in the mirror section is about wondering why the girl went for his friend when he thought he was doing everything right.
He’s a “Nice Guy” creep/villain.
Now the dude in “Is She Really Going Out With Him”?? That guy is about to snap.
I don’t see anything in the lyrics that make the speaker look like a villain, but I don’t know if this is a reliable narrator. I’ve been in Jessie’s girl’s position, and I suspect the friend of the guy I was seeing, had he written a song like this, would have also portrayed himself in a sympathetic light, when in fact he was rather creepy and obnoxious. Many of us have pined for someone from afar, but some should really pine from a little farther away.
That would be a hero vote.
Hero just means you don’t think he’s a creep trying to ruin his friend’s relationship. If you think he’ just a normal guy in a rough situation that’s “Hero”.
I should have included a voter explanation card 
Have you seen this?xkcd: Tag Combination
We need a sequel song where we get Jessie’s perspective on the whole affair. Sort of like Shel Silverstein’s “Father of a Boy Named Sue.”
Wow, THAT was a leap.
It’s the same thing I was thinking. The singer isn’t really interesting in Jesse’s girl. He’s jealous because Jesse has something that he doesn’t have. The song could just as easily be about Jesse’s car.