There are a lot of inconsistent or not very good textures in Minecraft so I made this list.

(All things have images)

Inconsistencies

Observer Top, Signs, Painting Back Sides, Toast Pictures, Recipe Book Icon, Statistics Menu Icons, Spectator Mode Icons, Inconsistent White Outlines, Hoe, Jungle Door item looks like the Jungle Door Block.

Issues

Blaze's Rods, Potion Effect Box, Brewing Stand Icon, Propper Block Brake Particles, Eating Mushroom Stew Particles, Iron Bars Z-Fighting, Floating Items in Hand, Stonecutter Rotates only one way, Villager Cloak, Hopper Bottom, Guardian and Smoker Pixel.

Ideas

Better Spectral Arrows, Soul Sand under Soul Soil Campfires, Better Tripwire Model, Nicer Fast Leaves,