For some reason my bounding box is always tilted when i import to unity. I've checked for loose geometry and everything but there's nothing.
If you are using armature, check if you have your root bone named Root, so SkinnedMeshRenderer knows what bone to use.
Note that after renaming your bone, your possible blender animations might be broken. To fix this issue follow the instructions here
Looks like you're using Blender. In Blender, make sure that the object has its rotation and scale applied to the mesh. In object mode, select the object, hit
Ctrl + A, apply rotation and scale.
While the mesh itself may look fine in Blender, the object that holds the mesh might be rotated or scaled. Blender will export the unscaled and unrotated mesh directly from saved mesh data without the object's rotation and scale applied.