I hate self-checkout. I hate the way it tells me I haven't bagged the item when I have, and then when I take the item out and put it back in, it tells me I haven't scanned it. Ugh. However, there are usually just a couple of cashier lanes open so sometimes I have no choice. Also, the cashiers can't seem to bag things properly.
I bring my own bags, and they still want to put just a few items in there. My bags will not break like the flimsy plastic ones. One cashier told me it would be too heavy to carry, but *newsflash* sister! I carry ALL the bags in at once, so it doesn't matter if the items are all in one, or spread out in ten, I'm carrying them all at the same time! (I have this thing about multiple trips to the garage - lol. If I buy more than I can carry, I leave the non-perishable stuff in the trunk until I go back to the garage for another reason).
Which brings me to the other pet peeve. I try to put perishables together, so I can take that bag in to be put away immediately. I will group all the cold stuff together, and they will still reach WAY to the back of the belt to put something else in that sack.

Drives me nuts.
However, I really hate it when they start interrogating me about my purchases. I don't mind a simple "oh, you must be having a party" if they notice I've bought stuff for DD's birthday, or even "how do you cook that" when I buy spaghetti squash (I have yet to find a cashier to knows what spaghetti squash is - every time I buy it, I get asked). However, the "OMGOSH what are you going to do with THAT?" and "Does you family really eat THAT?" and "Why did you buy so many of THOSE?" comments I could seriously do without. Just ring up the stuff and put it in a bag. Sheeesh!
I will go to self-checkout on purpose to avoid those questions if I have something odd, even if it's not something typically thought of as "embarrassing," because I know I'm going to get the third degree about it.