Instead of responding to trolling, just click on their name, click on Add to ignore list at the left, and walla, you don't have to see any of their posts ever again... Cuts down on the spam and leaves meaningful discussion in the thread...
TG is a short hand for 土共 in hanyu pinyin. To put it simply it stem from the land reform made by the CCP in the early days...anyway, it's a word game that netizens play with authority.