Kindness v. Courtesy

TJ brought up a good point today.

"What's the difference between kindness and courtesy," he asked via Twitter.

This opens the door to so many other questions.
Courtesy seems to me a sort of social obligation. It greases the wheels of society, as they say.
But courteous acts can still be done in the spirit of kindness. (They can also be done grudgingly, with complaints. This is something that I, personally, am guilty of.)
Maybe kindness isn't an action. Maybe it's an attitude. Maybe it's a way of being.

Acts of Kindness
21. Hung out with Robyn and K-San
22. Talking with Robyn (and trying to prod into her personal life.)
23. Complimented a girl's socks.
24. Told Josh about his change he left at the bar
25. Bought Hard Cider for me and James
26. Took Jeff to work

Acts of Kindness Done for Me
Robyn invited me to see a show with K-San
Neighbor at the job site came to check on me. Wanted to know if I needed anything.
James bought me a drink
Josh bought me a drink
Josh complimented my weight loss
My mom called to tell me about a place that is hiring