All of mine were developed over time and have reasons behind them.
My RIRs:
Hattie- she has a darker spot on the top of her head off to the side that looks like a little hat, plus she is the smartest and first to attempt flight, escape, and friendliness. She seems like a leader since everyone else copies what she does. She reminds me of Haddie from NCIS L.A..
PJ- stands for plain Jane because she has no discernible markings and she tends to just blend in to the flock.
Butterfly- my eldest son named her that because he swears the mark on her head looks like a butterfly...I don't see it, but I let him have it.
Nelly- because of all my chicks, she was the first to have tail feathers. I kept calling her tail feathers until my husband pointed out the song by Nelly called Tail Feathers...thus, she became Nelly (just in case she is a rooster too...haha!)
Dot- because she has a dot on her head and she is a little nutty like the character Dot from the Animaniacs.
My Barred Rocks:
Angel- she has a white spot on her head that is perfectly shaped like an angel...or a penguin, but that didn't fit her.
Fluff- because she is just this black grey ball of fluff still...I may switch it to cumulonimbus after the cloud and just call her Nim or Nimbus for short.
I also have two black sex links that I just got. They will remain nameless until something pops out and sticks.