Gumtree sellers who are "getting rid" of their small pets (I keep guinea-pigs) because the "kids lost interest/we're getting a puppy/ I don't have time"
People who take small babies inti the nail salon - I'm practically gagging and I sit by the door (my DD has her nails done not me).
"He's tired/hungry/teething" He's fucking choking 
People who put the most precious thing in their lives ie their child in the front seat when they're little. When they have three seats in the back and statistics show its safer to sit at the back.
There used to be an age limit of 12. Why did this change?
Patients who try to con me . They make their own appointments by phone . They get a reminder text or call ^2 days before". Then, they don't turn up. I have to give them 10-15 minutes leeway. Then I phone them. And I have to send out a letter . And phone our booking office to let them know. This, as you can imagine takes time.
So the call is "Hello Mrs Smith, this is "70" from the XYZ Clinic. You had an appointment with us at 2pm"
"Oh, no its for tomorrow"
"It; was today at 2pm, I have all the details on my screen"
"No, its definately tomorrow, she told me and I wrote it down. Definately tomorrow"
"Have you got your card , can you just check thanks"...........
"Oh, I have it here. Monday 5th @2pm. ...............Oh that's today"
"Yes"
"Well can I come up now"
"No, I'm afraid you've missed it and I have another patient in 5 minutes"
"Can you rebook me. I need to be seen, I can come up tomorrow "
"I'm not allowed to, I will send you a letter and when you recieve it, phone the office"
Then it comes ................ Oh well actually I'm not very well ...cough
And, I'm thinking : well enough to argue with me .
If I'm feeling generous I say "Well its saved you a wasted journey tomorrow" rather than saying "No you've wasted a precious appointment , it'll be 6 weeks before you get seen"