Trolls hate to be trolled back; the irony of troll picking
Earlier today I had a Twitch jungle. He said he was totally legit... so I picked Garen support. He was incredibly pissed.
Another time way back I had an AP Nautilus mid. I responded with Taric ADC. He was incredibly pissed.
Yet another time I had an Ashe top. I responded with Sona mid. He was incredibly pissed.
Trolls absolutely hate it when you troll them back. They only get off if you are playing serious and lose. If you are trolling right back they can't handle it. Just a protip if you really want to piss them off. Just do what they're doing, but better.
Had a Janna jungle awhile back, but didn't get a chance to counter-troll pick, I would have totally gone AP Draven with Lich Bane.