Ghostbusters headcanon pt1!
I always headcanon this, that Callie invited Egon to her wedding hoping he would have come but he couldn't and that Egon felt awful so he learned how to sew (thanks to Janine and her help) he sewed her a hand made wedding dress prob using his mother's dress he probably found from somewhere and stitched it up to make it look better and fit Callie, and sent it to her. Callie received the wedding dress and didn't wear it cause she thought that he couldnt show up to her wedding without an explanation but have "the audacity" to send her a dress as a "forgiveness present" so she didn't wear it the first time but when she got with Gary and was getting married (before the Frozen Empire events) she wore it to honor him.
Let me know what you think and with your own headcanons in the comments!