OK!
What really grinds my gears is when I'm browsing products on a site, see a pic of said product, and it encourages me to "click on the picture for a larger image".
So I click on the image and THE SAME FUCKING IMAGE pops up centre screen, the SAME FUCKING SIZE!
Or, even worse, it's the same image blown up into a pixellated mess that looks like something my dog vomited up!
Sometimes the lazy-arse person who made the site even reverses the image, so the original is LARGE, so you click on it thinking
"Wow, I'm going to see this product I'm interested in really HI-RES so I can REALLY check it out in detail!"
You click on it, and the thumbnail takes centre stage, in all it's 10mm x 10mm glory.
That really grinds my gears!