Яблоко раздора [yabloko razdora] - bone of contention
an incident or thing that may cause a quarrel, unexpected and negative, and sometimes dangerous consequences. An expression can be used when an object or thing can cause quarrels, conflicts.
Ясно как день [yasno kak den`] - as clear as daylight
obviously, elementary, undeniably, simply. An expression is used when something goes without saying