An individual that tries. Hard.
This is not in reference to those that are scholastically ambitious, or put effort into sports. No, no. This is a strong, biting description of someone that obviously thinks a whole lot about their
public image - fashion, vernacular, taste, etc. Such a person tends to fit very
neatly into a particular
pigeon hole - typically, a subculture. A tryhard is pathetically hyper-aware and irredeemably lame in their awareness and internalizing of all things external and obvious.