Green’s Dictionary of Slang

prefixed by a single letter, e.g. F, to denote a spoken but unwritten obscenity.

2013		Newser On Line 9 Feb. 🌐 Judge Forgives Teen Who Flipped Him Off. The Florida teen [...] flipped him the bird and dropped an f-bomb.
2021		P Howard Braywatch 11: [She] walked out of the church, lobbing fock-bombs over her shoulder.