When your team takes your lane hostage at 10 minutes and you only have 50-60 CS and enough for half an item.
When the ADC roams mid, doesn't get the kill, then sets up a tent in your lane, which consequently causes the enemy team to come mid.
Choosing between farming top/bot and hindering your team or being starved for the rest of the game while trying to help in teamfights.
Not to mention when your team dies to your enemy, then blames you at the end of the game for feeding them just because you're their lane matchup.
And if my constant pings to "please leave" work, the enemy is already camped with 2-3 people in my lane and I can't farm without risking death.
I really don't know what goes through people's heads, but I haven't had a good, 100+ CS laning phase in about 20-30 mid games.