Much like the slang word "sick" it can be used in both positive and negative scenarios.
In the positive sense it can mean fun, daring, chill, etc.
In the negative sense it can mean sketchy, wrong, or terrible
Positive: "Hey Demarcus, that party was majorly tretch, mann!"
Negative: "Yo man, we have to get out of here. This shit is hella tretch."
This is Tretch Dude!!!!"
" That party was tretch man, there was alot of illegal activity and I felt threatened by it..."