He could have just written a check for $800 and been done, but he decided to go to the trouble of getting 80,000 pennies from a bank. Loaded them in a trailer. Drove the trailer over to the ex’s house, and dumped them. Guy sounds super-immature.
No matter the circumstances of the divorce or the child support agreement, whether fair or unfair to him, what his daughter will always remember is that her father thought it more important to make a childish statement rather than just paying the final child support payment and perhaps now that she’s 18 and no longer getting support, trying to build a meaningful relationship with her. I think he probably burned that bridge.