It is not unusual but I am curious what you think about this. So, when you do a favor to someone but the guy forgets to thank you, will you say, "You are welcome" to remind him?
I do this all the time while I'm driving! I allow someone to cross or I allow another car to pull out and they don't wave to acknowledge and I say "You are welcome.....I thought one of us should say thank you!"
It depends on who it is. I usually reserve the sarcasm for strangers. Like, if I let someone get ahead of me at the store and they don't say anything I'll mutter "you're welcome" under my breath. I don't come across too many people who don't say thank you when they should though. The thing that a lot of people seem to be forgetting these days is "excuse me."
I learn to thank others from my partner. She always says it expressively and wholeheartedly with her nice smile and bright eyes, even when I (or other people) just do a little thing for her, like preparing our meals. You're most welcome, my love!
No, I don't do this. To me this would make me just as rude as the other person who didn't say it to me. I might say it to my kids to remind them to use their manners though.
It depends on whom I give the favor to. It makes me feel better when I receive a thank you or a smile, but it makes me humble when I don't receive an acknowledgment for a favor done.
You are welcome 
You're most welcome, my love! 
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