A lot of the more disturbing content isn't so bad, because it's lightened up by the humour - they managed to make a main character getting impaled on a pipe funny - but there are exceptions.
Lucy the shapeshifter using her powers. She looks like she is tearing her face off, at least the first few times, and it looks painful. (Similarly, Simon's power is apparently painful, according to his Twitter account - apparently he's 'getting used to it).
Tim, who thinks he is living in a computer game, calmly killing random pedestrians to 'earn points'.
Even worse, he reappears in series 5 trying to treat himself. But he finds himself slipping back into video-game mode, and is terrified he'll start hurting people again.
The Milk Guy in the series two finale - He can still manipulate dairy products after you have eaten them. And he is very creative. He can drown you with the yoghurt you had for lunch. You're immortal? Fine, he'll use the mozzarella from the pizza you ate earlier to give you permanent brain damage, leaving you as a vegetable for eternity. The last we see of Nathan, he's slumped over drooling.
In series 4 the gang gets trapped in a locked, dark room with a zombie.
The White Rabbit from season four, anybody? Considering that it was a hallucination from an acid trip, no wonder...
Emma in the series 5 premiere has an absolutely awful "power": she's unlucky. She slipped and impaled herself on a potato peeler, her coffee mug broke and doused her, and she gets hit by a car when crossing the road. Emma actually mentions that she's forgotten where all her scars are from, there's just too many.
A girl from the support group has the ability to turn things inside-out. She wants to lose it as she used it accidentally on her cat...
Leah possessing Alex and attacking the gang, particularly as the rest of them have slim frames and Jess is half his height. One moment you're with a friend, then he grabs a nail gun and attacks you.
Luke is a very disturbed man. He has the ability pull himself and others backwards and forwards in time. He uses this to steal a year of Jess's life, and to force her to be in a relationship with him. He says that if she rejects him, he'll just use his power to force her all over again until he gets it right. He also implies that he's done this before to several girls.