To have a sick alf is to have a messed up hair style.

The use of the word "sick" is used sarcastically to mean shocking or shit.
The word sick is used normally by people to imply Insane, Cool, or Crazy

See sick

The alf part of the comment is unknown of its meaning.
It probably originates from Alf the hairy puppet.

See alf

when you've done something so cringe you can't stop replaying it in your head and it stops you from getting on with your every day life