Trolls: Wandering in jungle @ 30 minutes when we are team fighting. People who just rage in pregame lobby because they didnt get mid so now they're gonna feed. People like that.
People who rage in pregame lobby because they didn't get mid and they feed are trolls and need to re-evaluate their position playing ranked. They won't, because they are likely children who had such a hard day at school they feel the need to ruin everyone else's experience.
These are the people that you just let them feed and report them after the game. The more you instigate it, the more they will want to feed and get more of a reaction from you. If they truly feed and get 9 reports at the end of the game, they will probably get banned. Just don't tilt - it will take you off your game too.. and probably piss off some of the other players who are spending their time trying to CS and lock down kills instead of typing/complaining.
In fact, I find it's good practice to straight up mute every person who you don't think will be contributing to your win. This means the entire other team, and anyone who has given you attitude in champ select. This means you won't even know about their bullcrap and you can spend your time taking advantage of every opportunity you can. Then down the line, when you're in the opponent's base and have a good feeling you'll win you can grab some popcorn and unmute them. The flame wars are real in bronze.
I haven't really been far outside of bronze so I can't speak from personal experience.. but I have some friends who are in the diamond/platinum range who have told me the trolls will decrease the further you go.
As to wandering around in jungle at 30 minutes when there are team fights - they don't know how to play yet, they're going for an objective, or they think the team fight is not in your favor. If dragon is up, and he's heading toward the dragon, let him solo it. If he's going for a tower, let him take it. Good players will take advantage of their whole team going bot lane and shoving top. If its a 4v3 in your favor, and he wanders the jungle, he's bad. If it's a 4v4 and he wanders the jungle, he's bad. If its a 3v5 in the enemy's favor, or if your team is pushed too far too early, they are avoiding giving kills to the enemy team. If they are flat out wandering around just killing camps while everybody else is team fighting, the player is just being bad. They aren't trolling, they're just bad.
Easier said than done... but don't flame them. Let them know they need to be involved and what they can do to fix it. Telling someone what they did wrong IN HUGE CAPS AND !!!!'s doesn't solve anything. If they still respond to your assistance with douchebaggery, then report them for bad attitude.
TL;DR - Bronze is famous for people who don't know what they're doing. Put 100% of your focus on your game, and don't be a dick.