Bond angle in water vs in oxygen difluoride
Water has a bond angle of 105º and oxygen diflouride has a bond angle of 103.8º, which cannot be explained by repulsion since fluorine is larger than hydrogen$[1]$. This is phenomenon is, however, explained by Bent's rule:


  Bent's rule is that in a molecule, a central atom bonded to multiple groups will hybridise so that orbitals with more s character are directed towards electropositive groups, while orbitals with more p character will be directed towards groups that are more electronegative.


p orbitals are oriented 90º from each other, so orbitals with more p character have smaller angles between neighboring atoms. The effects of this phenomenon can also demonstrated by comparing bond lengths.



$[1]$ Bent, H. A. Chemical Reviews 1961, 61 (3), 288.