This is an abbreviation of the expression "Hate My Foreskin", becoming widely used as a way of expressing one's disappointment, or feeling down in general.
Blaming one's foreskin is a lot harder to confuse for someone turning emo than the more popular HML
Guy 2 "Same man, HMF too"
2. a name given to those that cannot keep it in their pants.
3. one that is extremely enthusiastic about anything and everything related to sex and/or sexual pleasure.
"Oh, thats just KCoop, shes such an HMF."