Being perpetually absent minded when non-life altering things aren't right in my face. Especially when those things make other people think you're being rude.
Example: Last friday I had one of my "series of unfortunate events" days. I had at least three different tabs with various conversations open when firefox crashed. I restarted the computer and started messing with other stuff, telling myself I'd come back to those things later. Cause, yeah, my brain goes "Oooh! Shiny!" and runs off in random directions when not corralled. On top of that there are kids, dogs, housework and other offline things to take my attention and slip ups happen. This slip up just meant that I have at least 5 different on site messages from three different sites I thought I had responded to and it looks like I actually did not. I'm back tracking right now and making sure to get back with everyone.
So, yeah, if you sent me a message last friday night, or possibly even last saturday, I'm so sorry for not getting back to you and am playing catch up when not distracted by the shiny.