What Do You Do?

There are 5 scenarios presented below:

Scenario A
You treat your friend to a meal.

Your friend doesn't finish even half of the food ordered, saying that the food is disgusting.

Scenario B
You offer to pay for some stuff together with your stuff when you two go out buying some stuff. The money's not a lot - maybe less than $10 or so.

You think that (on good faith) your friend will return you the money soon, but somehow the issue of returning your money just seems to be the last priority for your friend, even a few weeks down the road.

Until it seems like you have to remind your friend constantly (like a loanshark) so that you can have your money back.

Scenario C
You go overseas for a short trip, and you think of buying some small items for your friend. You end up buying some local delicacy which should be pretty good enough as a gift for your friend.

So you bring it back and gives it to your friend. Your friend thanks you for the food.

Nothing else happens thereafter.

Scenario D
You meet your friend for drinks, and you offer to pay for the drinks for your friend. Your friend says the next meal/drink will be a treat to you in return.

The next meal/drink comes along. It never happens.

Scenario E
The above 4 scenarios refer to a single friend.

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What do you do when you are faced with the above scenarios?