Now I know for one there is lore behind each and every class combination in the game. Of course, I do I am a huge fan of the lore of WoW. The thing is in practice I find the look of some of these races and classes in game look just beyond weird. Maybe it has to do with the actually gear design was not thought about when it was designed with a particular race in mind, but still that really isn't an excuse. Here are some of the ones that make me facepalm whenever I see them.
Gnome Warrior: Warriors are supposed to be fierce and strike fear into the enemy. Be able to tank mammoth beast, demons, and constructs still while being the machine that they are. So explain to me how a 3 foot tall Gnome is supposed to achieve this while the enemy is 1000x their size. This isn't even as much as the gear even if it destroys the look by being so tiny. I put gnome warriors in the same group as Tauren rogues, they don't make sense. The difference is Tauren Rogues are not actually a class in game.
Tauren Priest: This has nothing to do with over sized gear or anything like that. This is the gear design is always so elegant and clean cut and sparkly. This design doesn't fit the tauren at all. A former nomadic people which still are in the roots of that society. Now tauren priests are great and a wonderful idea and fit into lore great I just find the gear styling doesn't fit them at all and the only fix would be tauren priests themselves to have a different gear set.
Draenei Mage: Now this isn't entirely true with the female draenei it doesn't bother me at all. When I see a male though I just get the blue version of the Game Genie guy from the original Nintendo. Maybe it is their animations that just bother me but they just don't fit with what a mage should be.
Worgen Druid: Yes worgen druids are fine. My problem is when you are a druid before you actually become a worgen and you are a human druid. The weirdest thing in the game in my opinion is watching a human casting wrath.
Blood Elf Anything: They just look wrong as anything and everything.
There you have it. Those all just look off to me. Did I miss anything, if I did I am sure you would tell me.