Turtleneck is a slur used to describe French in a derogatory way. Many of the French are uncircumcised.
The word Turtleneck is a racial slur that has been used historically to degrade and dehumanize french. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to french. If you are unsure about whether or not it is appropriate to use the word Turtleneck, it is best to err on the side of caution and avoid using it in any situation.