f&f
Fast and Firm is like a brotherly greeting, used when you sign off a letter to your brother, like you're saying "dear brother" but with more swearing.
"I'm signing off with fast and firm, because I'm being a total idiot."
"I'm signing off with fast and firm, because I'm being a total idiot again."
"I'm signing off with fast and firm, because I'm being a total idiot for the third time."