Facebook: UI doesn't fit with Android standards, and on top of that it sucks too. An example of how to get it right on Android is the Google+ app. They should really be using the standard action bar (or at least a better emulation of it), and the standard navigation drawer. Facebook had an update for the iOS7 visual standards on release, but they still haven't fully embraced the Holo themes introduced 2 years ago on Android. In fact, the Android app's UI is essentially just bad port of how their old iOS6 app looked.

Poor performance overall, this has gotten better as they've switched to a more native UI, but it's still worse than it should be. Scrolling performance is still a bit janky, even on the Nexus 4 - A few seconds with overdraw shown gives plenty of things to fix.

The Image upload UI is pretty bad, especially that horrifically designed notification.

Twitter has similar issues, mostly to do with using non-standard + bad UI. They have a beta version now with a faked Navigation Drawer, but they got lots of things wrong so feels really out of place (why they didn't use the standard one is a mystery).

Overall, the FB + Twitter Android apps clearly get a lot less love than their iOS apps. They have actually been getting better - the facebook app a few years ago was far worse (e.g. couldn't see or add event comments, which is pretty obviously important on mobile), but they still have a long way to go before they match up to the quality of the Google apps on Android (some of which I have problems with also, but that's a different issue!)