Here are my worst:

1. Having a sip of the brown water you are cleaning your brushes in , thinking it was that nice glass of tea your poured.

2. Finding all the pieces necessary for a section to dry fit, then going back to the instructions 4 or 5 times to remember what order they went together in.

3. using the pliers on a tough piece of sprue, just to slip, cathing the skin of your forefinger in the vise, resulting in a large blood blister.