i don't know what this file might be.
please open a terminal in the folder where it resides, and type
cat rockyou.txt | more
this should not freeze your system and give you an idea what you have there.
if it goes on for many pages (advance by pressing space bar) and contains weird characters - and you are trying to open it with a stupid gui text editor that does not secure itself from this sort of overload, well then there's your system freeze.