Maybe this is better off in the pet peeve thread, but people who "like to paint" but don't have a frikkin' clue how to do it piss me off.
My neighbor wanted to help with one of my projects (exterior - latex paint) because he "likes to paint."
I assumed that meant he had some idea how to go about it.
Me -I hate it. I hate the prep and I hate the cleanup, though I actually like flowing the paint on. So I said, "Sure, it'd be great not to have to do it."
So - he starts by opening the can.

I had to get out the brushes and the sprayer, lay down the drop cloth, and get out a 4x4 slab of old plywood for him to work on so he didn't spill paint all over my driveway. Basically I did the prep.
What he was painting was a structure akin to a jungle gym. So his "plan" was to start on the outside and work his way in to the center.

In the meantime he managed to spill paint on my driveway anyhow, got paint on the side of my barn, on my barn floor, and left paint for me to step in - by the time
he finished painting
I had paint on my hands, my shirt, my shoes, and my truck. When he finished with the sprayer he put it in the shade and took a two hour cigarette break, then couldn't figure out why it was stopped up.
Took me half an hour to clean out the damn sprayer. I had to throw the brushes away.
I could have done the job myself in less time, I wouldn't have gotten paint on everything in sight, and I'd still have two good brushes.
Next time someone wants to help me paint I'm going to tell them it's too damn much work to have help.
End of rant.