Cut off in a haphazard or aggressive way. So in this context I would picture the haircut being really uneven and maybe messy- looking. But in a stylish/punk way I guess since the narrator sounds happy about it.

Hacked off is normally a phrase used with negative connotations. It is normally used to infer that someone is unhappy, annoyed, or irritated, especially because of a situation that they find themselves in. He was really hacked off when they lost the game. She’s getting a little hacked off with all the travelling she has to do. In this example when you hack something off (in this case the womans hair) it means it has been cut off with strong, rough strokes normally using a sharp tool or implement, such as an axe or a knife. so not evenly or neatly. Kim hacked off her long hair.

To hackl is to roughly hue. Roughly can mean aggressively, or it can refer to the result being rough, less than scuptured. For hacking wood, into a shape: Think chainsaw rather than artists chisel. . "Hacked off" can also mean annoyed in some places. From context, this is not the case here.

Usually would be an exaggeration of something you didn't like.