Be careful not to confuse "buying lunch" with these similar-sounding idioms:
: To outcompete or take an advantage away from a rival.
To "" literally means to pay for their meal. However, as a social "feature" or gesture, it serves several deeper functions: 1. The Professional "Brain Pick"
It is a casual way to thank someone for a small favor or extra effort. 3. Romantic Interest (The "Date" Offer)