So as a JG/Sup main (I must be a masochist or something) nothing is more frustrating than someone pinging to keep me from taking farm that it would be impossible to get.
Example 1: I'm jungling and my Orianna mid dies to Katarina under tower. I do what a jungler is SUPPOSED TO DO and head mid to hold the wave and last hit the minions. As I'm LAST HITTING (NOT pushing) the minions under tower, Orianna pings me like a fucking madman while I'm last hitting saying I'm taking her farm. What she fails to realize is that its better for an ally to get the farm than for NO ONE to get it and just let it die to tower. She would not have been able to get the wave in this situation so last hitting it until she returns (That means until she comes WITHIN AA/Ability range of the current wave) was the right choice, so don't ping me for it.
Junglers hold your lane after your death to minimize damage to the tower and soak up the XP/Gold you would've missed while you were taking your free trip back to the fountain. Towers don't level or buy items, so if the tower will kill the minions then let your jungler take the wave when you cant.
Example 2: I'm Sona support with Vayne adc. We're against a Tristana who pushes lane as the cannon wave is coming in. Vayne is out of mana and JUST finished an AA on another minion but the tower shot that will kill the cannon minion is mid-flight. I quickly use Sona's Q to secure the cannon (since Vayne was physically unable to) and then she starts question mark pinging me telling people I'm trolling and stealing farm. Had I not last hit that cannon minion WE BOTH would've missed that gold so its better that I take it than no one, yet I get pinged like I did something wrong.
Supports aren't supposed to take an adc's farm (obviously) but if the adc misses a last hit by a small margin/doesn't AA and the target will die to minions, is oom, or cooldowns are spent, then the support SHOULD be taking the minion so that at least one of you gets it.
Stop pinging people for taking farm you are completely unable to get. It's dumb and defeats this game's entire purpose. (Amass gold to get strong so you can break the enemy nexus) Lose the attitude of "IF I CANT HAVE IT, NO ONE CAN!" and learn how to think as a team, not just for yourself.