I'm an administrator of an English-language online community, and a user has a username punning on the word "merde:" "merdehappens."
We accept mild profanity: "crap" would be fine, but "shit" probably wouldn't. The general rule is that we want people to feel welcome and feel like the community is a safe space.
How vulgar is "merde" when used outside of a longer phrase?
Some web searches suggest that "kids don't get in trouble for using it" but I'm not sure how reliable those are. What would French-speaking people think of the appropriateness of "merde" in a mixed-ages (13+) community?