Because of the word "f*cking".
You have to stop using profanity altogether in order to remain SFW, not even censoring helps.
I don't agree with this, because:
1. Imgflip is a 13+ site, meaning that the content is not supposed to be for kids, so protecting kids from content from a site they shouldn't be using, to begin with, is a waste of time.
2. The word was already censored, meaning that additional censorship is unnecessary.