Sure, it would bother me. I never claimed to have perfect middos. I don’t think I’d rant about on YWN, though.
Your case is also much worse. Driving off without simply saying thank you on the spot shows a lack of hakaras hatov a lot more than not going through the hassle and expense of thank you cards. I guarantee you that if the person who possibly didn’t send out the thank you card would have had a flat tire, he’d thank you profusely for helping him to change it.
I don’t know why you say I lack manners. I didn’t say you shouldn’t send thank you cards; you should. I just don’t think you should stew in indignation if you don’t receive one.