Utawarerumono perhaps?
Hmm what irritates me..
When the main character is so extremely bland in his design that there's no personality to him at all. Like the pure opposite of Yugi & Co. Usually that means the character is made as an audience insert though, and I tend not to watch those shows because they turn out to be harems most of the time anyway.
Or as I mentioned in another thread: Extremely shy girls wearing revealing outfits. It. Breaks. The. Character's. Logic.
Additions to a design that completely defy logic, reason and/or sense in the story. Not if everything is a bit over the top, it works in-universe. But when you have one random thing, like Mouri Ran's horn... I swear that thing just gets more ridiculous as time passes. xD
Everyone else's hair is perfectly normal though.
Ps. I have no trouble finding plain tees... You just have to look in the basics department of stores like H&M, Bershka, Zara etc. (or Uniqlo, if you're lucky to have one where you live). Trust me, I work in a clothing store haha. I'm in Europe though, it might be different where you live.