"Rad" – unless it refers to a radiator, and even that's debateable.
"Off" – as in "Tinners was pedalling at walking pace along the bridleway in perfect conditions when he had a nasty off" – "**** off" I can understand, but "nasty off", "big off", etc make no sense to me at all.
Unconventionally spelt names e.g. Lynda and Walliams, lovely though they are, because I always get the spelling wrong.
Names that can be pronounced a variety of ways e.g. Aaron (lovely name, but is it "Air-on" or "Arghh-on"), mainly because I always get the pronounciation wrong
Surnames with a "z" where you don't expect it e.g. Gzbowska, again, lovely in themselves, but for the sheer inevitibility of either causing offence or looking foolish or both when trying to pronounce them.
"Bad" – see above, as in "my bad". Your bad what? Grammar?
"Niche" – as in "That bow tie and toupe combo, Mr Tinners, is very niche"
"For my sins" – having invariably described something that is about as sinful as picking daisies.
"My better half" – only because it's usually accurate
"Nom, nom" – unless said by somebody who genuinely leaves their dentures out and pinches their nostils whilst eating sticky food.
"So" as a means of gauging a unit of measurement – as in "It was so high and about so wide" (usually accompanied by a "pincer" or "arms held far apart" gesture)
"So" – as in "I'm so over him/That's so 1990". Usually accompanies a "like" e.g. "Thats so, like, 2009"
"One" – unless it refers to a number and not oneself.
"Lush" – unless it refers to dense green vegetation
"Strength in depth" – because no rugby commentator can go 5 minutes without saying it
"Old age doesn't come alone" because whoever says it thinks they're the first to have said it.
"Hubby" – You'll never hear a bloke refer to himself as that, unless the wife wears the trousers in that relationship, if you know what I mean. (However, fascinatingly, if the wife uses the term "Hubby" then it often indicates a relationship of "his n hers" things where they both wear identical brands and styles that only differ in colour – e.g. both wear matching cardigans/walking boots/MTBs/lederhosen/golfing apparel etc, but his is in blue, hers is in pink – am I the only one to notice that? It's a practice that's popular in the over 60s and often sighted in the Lake District).
"Nipple" when used to describe anything other than the ends of ladies boobs. As in "Have you tried pulling on the nipples, Mr Tinners, before you release the grub flange holding the stanchion bracket on to the pawlgrips?".
"Pawls/stanchions" – because I don't know what they are, what they do, how expensive they are to fix and they sound like words that have been made up just to confuse me.
"Her/She" when used to describe a mechanical object. As in "She'll run a lot more smoothly after you've lubed her up" (said pointing to a bike/car/tractor)
"In the zone" when used to describe a rider who isn't riding along a designated area (Disabled/Mothers and toddles/No parking) marked out with yellow cross hatched chevrons. As in "Tinners was riding like a God along the singletrack switchback and breaking all records because he was in the zone".
I could go on.
