Did Charles Darwin have any nicknames?

Stinky Pants, I believe.

Darwin's nickname was apparently "Gas".

Not for the reason alluded to by mandelbrotset, though. It was more to do with his penchant for conducting noxious chemistry experiments in his shed.

Eras (his brother) took an interest in chemistry and Charles became his assistant, with the two using a garden shed at their home fitted out as a laboratory and extending their interests to crystallography. When Eras went on to a medical course at the University of Cambridge, Charles continued to rush home to the shed on weekends, and for this received the nickname "Gas".

https://en.wikipedia.org/wiki/Charles_Darwin%27s_education

He would often sign his letters to scientific friends as "Stultis".

This name referred to his habit of trying experiments most people would prejudge as being fruitless or a fool's experiment.

This site suggests he had numerous nicknames:

"Philos" while on the HMS Beagle.
"Flycatcher" when he was collecting specimens.
"Sage of Down", "Saint of Science" by journalists.
"Czar of Down" and "Pope of Science" by his friend Thomas Henry Huxley.
"Stultis the Fool" a nickname of his own choosing, and he often signed letters to scientific friends with "Stultis." This name referred to his habit of trying experiments most people would prejudge to be fruitless or fool's experiments.

"Gas" in a previous answer seems to be an accepted nickname too.

https://www.papertrell.com/apps/preview/The-Handy-Science-Answer-Book/Handy%20Answer%20book/Did-Charles-Darwin-have-any-nicknames/001137021/content/SC/52cb031f82fad14abfa5c2e0_cool_facts.html