Following Gaz and Donna's (first) break-up due to the former sleeping with Janet, the two of them have to pose as Jonny and Janet so the latter couple can get married (It Makes Sense in Context). Cue Donna-as-Janet's original wedding vow to Gaz-as-Jonny:
Donna:(completely deadpan and straight-faced) My darling husband-to-be. Ever since you shagged my best friend and got her up the duff, I can think of no better way I'd rather spend my life than with a bastard like you.
(Cue the registar looking on in disbelief)
Janet:(in labour) How the hell does a baby's head come out of something so small?!
Jonny: Small? You think a lot of yourself.
Louise: You must know all about prostitution, Donna, what with your mum being a whore.
Donna: My mum wasn't a whore! She just had sex with men... for... money...