This isn't exactly a modding mishap but it's along those lines.
I saw in my Alerts that someone had asked a question about my mod, so I quickly jumped to it and answered their question with a quick back and forth and forgot about it. Then today I was bumbling through the site and came across my back and forth....on someone else's mod page....derp. To be fair our mods are almost identical. So, I had seen an Alert for someone else's similar mod and just jumped in as if I was the author....which I thought I was....just not that one specifically. Anyways I kept saying "my mod" and so on looking like a giant douche bag. No body seemed to notice except me so that's cool. At least I was helpful.