Shaco's E (Two-Shiv Poison) bug
Sorry I don't have any video proof of this, but I did get this bug a few times:
When you try to E an enemy who's about almost in a bush where you have no wards, the E's animation starts (the dagger is thrown), but it deals no dmg and your ability doesn't go on cooldown. I don't know how hard it is to recreate (I'm at work), but I got that bug a few times and lost kills because of it.