Boche is a slur used to describe Germans in a derogatory way. The French called the Germans this in WWII. "Boche" is short for "alcaboche" or cabbage-head.
The word Boche is a racial slur that has been used historically to degrade and dehumanize germans. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to germans. If you are unsure about whether or not it is appropriate to use the word Boche, it is best to err on the side of caution and avoid using it in any situation.