Ok so how in the world do I deal with tanks as a mid laner?? Are there any mid lane champs good against destroying tanks? Tanks are just the most annoying piece of shit, they can go like a few damage items and full ass tank after that. They are tanky, have lots of cc, AND can still deal a decent amount of damage. Please, any tips on what mid lane champs can deal with tanks?
for tanks you want sustained damage not burst.
Role over and take it because you lose, tanks are just stupid right now thanks to items like 
this counters all AD champs, and 
counters all freaking AP mages.
Sure you can poke and poke and poke, but unless you get a gank, and a really good one at that, you likely won't be able to beat the person because they will play passively so you are forced to have to all in them or risk just giving them free farm.
Your talking to someone who will get full CDR, and full Magic Pen for the hope of being able to do something, but in reality, they just heal up the damage you deal poking them.
Taking a tank mid lane is so douchey tbh v.v mages aren't meant to be able to 1 on 1 a tank, yes there are things you can do, but all of them revolve around the fact that past level 10, you WILL NEED HELP to kill the person. SO the lane becomes a stale crusty farm fest of a passive tank and a mage who can't hurt the tank without help.
Rush 
and then go semi-tanky yourself and try to get some CDR in there too, so 
would be okay as well, but honestly, the situation is just FUBAR at that point.
like the other poster said you want sustain damage not burst vs tanks, tanks are design to survive burst. that is why adcs are great at melting them cuz they do sustain damage.
but that being said you need to look at what kind of tank your facing , are you taking ignite ? do they have big healers ? there are lots of things that play into that. you need to use the tab button in game and view what they are building and when and adjust your build accordingly . like of they are rushing MR then you need to rush MAGIC PEN.
but an over all good build vs tanks would be something like this
also what kind of masteries are you running, 12-18-0? 18-12-0 18-0-12? remember % magic pen good vs heavy mr and flat magic pen better vs low mr.
depending on lane you can go with a rune set up of flat magic pen marks, hp per lvl seals, ap quints, and ap per lvl glphs which will help your late game damage.
Rush
also you need to focus your burst as an ap mage on their ap damage dealer or their adc or support , eliminate one champ you should easily be able to do so as a full damage ap mage with one rotation of spells. after words you can then worry bout the next target. let your adc melt the tank while u take out threats that could harm ur adc. that is where target priority comes into play. sure you and ur team can focus the 4000hp sion and waste everything on him.... or you take out the adc/mid/support (squishy) and make it fight that the #s are in your teams favor. this is where things like damage foresight comes into play. you dont wanna waste everything on killing a sona, but you need to know what you need to waste to kill her and save your ignite and other cds for the tank or the next target.
