Is it reportable if your support intentionally takes cs/doesn't let you farm? I see this a lot in low elo. People get autofilled and are bitter over it play a mage and go full ap while clearing waves and denying the adc tons of cs. I even ask them if i can farm, and sometimes they straight up say no and start to troll me by taking all the cs.
No, nobody owns the farm. The support can take CS if they want.
Is it reportable if your adc takes all of the cannon minions when you have a 
?
Intentionally taking the cs after they got filled, If they refused to play their support role, then yes that is reportable.
Otherwise no, because no one owns any gold on the map.
Supports who tax are not only griefing, they are not being a team player and lowering your team's chance of success because ADCs are item-reliant and therefore need the gold more than any other class. Supports have items that generate gold for them and don't scale. Even if they are playing a mage support, their abilities base damage, range poke and CC is enough to contribute to the team, their damage is in levels mostly, not items.
If they're taking it all and doing so on purpose, then I'd argue yes it's reportable. If they have relic or take a few here and there when they try to land skillshots and poke onto the enemy team, then no. Lastly, if you are performing utterly horribly and they are not, then I'd say give them the farm because they will do more with it. But if you are doing poorly BECAUSE they aren't doing their job to support/protect you or you are doing well, then they should be reported. It's no different than the people who hold champ select hostage because they ARE GOING TO play THAT role and nothing else or the ones who ban any champ you show you want/plan to play because you got their role and wouldn't trade and often also get their duo friend to ban you out too.
That kind of behavior is toxic. It is griefing. It is unacceptable.
If my adc is shitty at CSing hell yes im going to take CS. why the fuck let it go to waste with the players inability to last hit. Might as well pick up their slack like a support is suppose to.
If they're doing it purely out of spite because they were autofilled, then yes. It is reportable. It is well-accepted that, during the laning phase, the support avoids taking farm from the declared bot laner. Because the player is doing it, not out of some agreed-upon strategy, but out of intent to "punish" other players on the team, they themselves qualify for punishment by Riot's rules (i.e. Don't be a jerk).
Obviously, there are many caveats to that. A player might accidentally take a few CS, or not realize the AD was in range after returning from base, or as part of a relic shield proc, etc., none of which are punishable by Riot's rules.
The only time I would tax cs as a support is if Im playing a AP carry support which I like to do in low elo AND my adc is really bad AND we are losing lane hard, AND is in no way gonna carry this game, so as a result I step up and start to take CS so I can in turn carry what is upto that point a losing game. Its worked out of me and my team several times.
