drop in on someone—(coll.) visit a person, usually without having arranged it before:
- I dropped in on her for coffee the other morning.
drop on someone—(coll.) reprimand or punish a person:
- You’ll have to mind your p’s and q’s or else you’ll be dropped
Note: The expression does not correlate in meaning with the phrase fall on someone—
1. attack a person:
- They fell on me like an avalanche with teeth and dagger, and hatred without check or limits of sanity.
2. used of a cost, responsibility, etc. to be borne by a person:
- So it fell on me to do all the packing, making sure we had all the necessary equipment.