Where you're desperate to swear, but can't form the words, and so use the first thing that pops into your head.
"Pobum" - when trying to say "Fuck you."
"Spatula Corsa" when trying to say "You fucking twat, you just cut me up in your shitty little Corsa."
"Trolley cunt beer mug" when trying to say "Oh Christ, Tekken is hard!"
To all of these, anyone listening might respond: "Wow, that's some completely random swearing!"