Jackass is my current favorite word. Not "jackass" as in let's-get-naked-and-throw-ourselves-off-of-ski-jumps jackass. I doubt the actual four-legged variety jackasses would want those guys associated with their name. This is the use of "jackass" that I love:
I was riding down in an elevator to my parking garage last week after work one day. I was behind two women who carrying multiple boxes and papers down the escalator in my building. They struggled through the door of the building with the cargo (I made appropriate helpful gestures along the way) and then got onto the elevator with me. After she pushed the button for her floor, one of the women said to me and the other woman in the elevator, as if she just thought of it, "I'm such a jackass! I have one of those wheely cart things right behind the door of my office upstairs!"
For some reason this really cracked me up and I've been using jackass as often as possible ever since. It is a nice alternative to "asshole" rush hour commutes home, I have found. And I look forward to calling myself one the next time I do something stupid (as if that ever actually happens!).
So try out "jackass" sometime if you are tired of or bored with your current fall-back insult word. It will not disappoint.