Flflfl is an elegant form of keyboard mashing. It's most often used when one wishes to express discontent with a certain situation without undermining the semblance of one's own grace and dignity. More anger can be expressed by adding additional repetitions of the letters "fl."
Lowly commoner: ARG! This day sucks! OEFJKMLDNFKDCMLS
Refined gentleman: Oh, my. I do not like my immediate surroundings. Flflfl.
Angry refined gentleman: Good heavens! It appears that my wife is not faithful! Flflflflflfl!
On an post online, Jack sees that he by liking the post, he will be the first liker, and if he comments the first commenter. So he comments, "flfc" to let people know that HE was in fact the first liker and first commenter.
person 1: did you know that you can type ¿˘¯Â˜ı◊Dz¸ÆÚÒÔÓ˝ÏÎÍÅ»’”∏؈¨Áˇ‰´„Œ±—‚·°‡flfi € ` if you type your entire keyboard backwards while holding shift and alt?
person 2: that's nice