When my manager tried to pay for my lunch, I declined and paid myself (I am from Russia, we had no such tradition at that time). The feelings I had were a mix of: a) is he trying to make me a teacher’s pet? I am not a teacher’s pet; b) is he trying to show that he has some power over me except paying my salary? At lunch break? He has no power over me except paying my salary, I can well afford to buy my own lunch.

An American visiting from other company was completely dumbfounded: Why have you paid yourself?? He is your boss, it’s his responsibility to pay when he invites you to lunch!!

...And I was completely dumbfounded observing his reaction: have Americans no pride?

Why are you suspicious of a coworker buying you lunch?

I sure would be. Why would someone spend that much money on me unless they're a closer relation?

Buying small gifts for coworkers is one thing, but buying lunch is a bit much. I wouldn't spend more than $5 on a gift for a coworker.

Cuz he's making, presumably, the same amount of money I am (or in the same ballpark). So either he got a raise, or he has an agenda...