The full form of smfh is shaking my f##king head
The acronym “smfh” means “shaking my f##king head.” It is normally used in response to a comment during conversation that the other person finds to be so dumb that they cannot find words to say in reply so they “perform” this action instead.

Origin of SMFH
Although the exact origin of this acronym is uncertain, it is an extended acronym of the original “smh.” The origin of the original “smh” is unknown as well. “Smfh,” “smdh,” and “smmfh” are all variations of this original acronym for those who prefer to state the original with some added profanity.

Example Conversations
Friend 1: Did you see what James did today at lunch?
Friend 2: No I must have missed it. What happened?
Friend 1: We were sitting at the table and him and Eric were arguing. So, he picked up a grape and threw it at Eric. It hit him right in the forehead.
Friend 2: Smfh! That’s hilarious!