As I mentioned in the top five post, WCW had a plethora of bad entrance themes. But that organization's general weakness helped to prevent any of their themes to be noticeably worse than the others. So while I don't think much of Ric Flair's or Glacier's or Dean Malenko's theme, they weren't conspicuously worse than the other themes you'd hear while watching Monday Nitro.
The WWF/WWE, however, has had some great themes, and by contrast, some really, really bad ones. Here are the five that in my experience have stood out as just terrible.
Honorable Mention: Right to Censor
I'm not going to put up a link to this "song" because A) it's miserable, and B) it's not really a song. It's just a bunch of alarms. It made sense thematically, but it was just brutal to listen to. I don't know who signed off on playing that 1-2 times a night, but they should've been fired.
5. The Shield/Roman Reigns
The Shield's version is slightly less appealing, but they're essentially the same song. The song has no rhythm, no excitement, and no flavor at all. Reigns also still has the gimmick of coming to the ring through the crowd, which is equally stupid. It wasn't cool when it was The Sandman, it wasn't cool when it was Raven and the Flock, it's just not an interesting move. In today's wrestling world, we should be able to demand a higher standard of quality when it comes to entrance music. It's not offensive, but it's bad.
I wouldn't have even thought that this was truly a "song," but when I check out the WWE soundtracks on Spotify, right there is Earthquake. It's basically just a slow march with rumbles around it. Unexciting and just not good.
I don't know what was wrong with Edge's initial theme song where they felt they had to change it. It wasn't amazing, but it was solid, and most importantly, it didn't sound like noise garbage. I'm sure some other people enjoy this theme, just as I'm sure some people enjoy this kind of thrash metal, but I am not one of them.
2. Billy Gunn "Ass Man"
This was during the WWE's period of trying to push the envelope sexually, with the premiere of the Divas as a regular part of the show, Val Venis who apparently came to professional wrestling by way of hardcore pornography, and as the counter, the above-mentioned Right to Censor. Billy Gunn's gimmick was an odd twist on "Bad Ass" Billy Gunn where...well no actually, Gunn was basically the same, it was just a weird, ill-fitting song. The tune itself is boring, with a particularly irrelevant beginning. No pop at all.
1. Rey Mysterio
Mysterio's theme song sounds like a nine-year-old kid put it together. The opening, which in wrestling is perhaps the most important aspect, is just completely dorky and dumb. I don't even know if the rest of the song is that bad; the beginning just kills me. That Mysterio was as popular as he was for as long as he was is a testament to the excitement of his wrestling style; he accomplished it in spite of having a terrible, terrible song.