Worst mistake:
Buying 3 straight run chicks at TSC, thinking I had 1 chance in 8 that they would be all cockerels.
Consequences:
I ended up with all cockerels. (I think "straight run" means they can't tell if it's a pullet, ie, it's probably a cockerel.) At 4 months, they became hormonal teenagers, harassing the 3 pullets I also bought, to the point the girls wouldn't get off the roost. They also became aggressive with me.
How I fixed it:
2 of the 3 had to go. I didn't have anything set up for culling them, so I caught them in a fishing net, took them behind the coop, and shot them. Then I cried, hard. It wasn't their fault they were male. I buried them in my garden, and I thank them for their contribution to the soil.
What I learned:
Do not buy straight run unless I have a plan for dealing with multiple cockerels. I will apply this lesson to hatching eggs, if I hatch some. I generalize this lesson to be: have a plan for ANY bird that doesn't work in my flock.