Clive
Cloe
Cloey
Clone
Clooney (after the actor George Clooney)
Clorox
Cloud
Cloudwalker
Cloudy
Clouseau (after Inspector Clouseau from the Pink Panther movies)
Clouseau (after the character in the Pink Panther movies)
Clove
Clover
Clovis
Clowie
Clue
Clues
Clumsy Cat
Clyde
Clyde Guy
Clydester
C'Mell (character in sf story by Cordwainer Smith, "The Ballad of Lost C'Mell")
C'mere (as in "Come here")
Coach
Coach Potato
Coal
Coaldust
Coalport (after the English china company)
Cobarde (Spanish for "coward")
Cobber
daddypa