There are many little things, I just don't feel that Android UI is as polished. I can live with them or in some cases I probably can customize things, but it's still irritation.
Here are some random ones:
* When I have to enter pin (6 digits) I must press "OK". iPhone unlocks after 6-th digit automatically.
* It seems that Android app developers prefer the ad model. I don't have a single app on iOS with ads. Yet it's hard to find a single app in Android without ads. And I hate them.
* I spent something like 30 minutes trying to add a second phone number to my own android contact. I did not succeed. Theoretically I have to go to Google profile and add it there. But that button was not there. With iOS me is just another contact that I can edit as any other contact.
* To turn off all radios (airplane mode) I have to swipe from top, then swipe again to uncover the full menu, then swipe again to go to the right menu and only there I can click to enable airplane mode. With iOS it's one swipe and one click. I guess that I can customize this screen with Android and I can't with iOS... I don't want to bother, actually.
* I hate back button philosophy. I don't want to switch to other apps with back button. I prefer back buttons in app UI.
* I can't tap top bar to scroll to the top. Some websites provide that button as part of their UI, so may be it's just an iOS habit.