Here's why:
* Collocation refers to words that typically appear together (like "heavy rain" or "strong coffee"). While "loving slap" might sound odd, it's not a violation of typical word pairings.
* Connotation refers to the emotional and cultural associations we have with words. "Slap" inherently implies aggression and pain, even if it's meant to be affectionate. The word "loving" contradicts the inherent meaning of "slap," creating a clash of connotations.
Therefore, the phrase "loving slap" is problematic because of the clashing connotations, not because of incorrect word placement.