Ah, that reminds me of a story.
My mother and my father were best of friends and all that noise, yeah? Then my mom got pregnant (little baby ❖!) and was "strongly encouraged" to drop out of her parochial high school. She transferred.
A few months and a few baby name books later, I was born. The two never really broke up, they just stopped seeing one another. So I've got no ill will toward the guy. From what I understand, he pays Child Support on time (usually) and once I spoke with him over the phone but we live miles apart.
Perhaps this year I'll buy a card, and then carry it with me for the rest of my life. If, by chance, I stumble upon him in a convenience store or a... monster truck derby or something, I'll deliver the card. It'll say "Happy Father's Day, thanks for the teeth"