What makes a melody 'aggressive?'

Questions about producing? Ask them here.
What exactly is it that makes 'hard' music sound 'hard'? Chords? Bass? Melodies?

I have yet to nail it down but I presume it's a mixture of low bass, noisy hats and snares, a simple and repetitive melody under a minor key, and lots of effects.

(Edit: 2000th post!)
IN the words of travis scott , Its all about the drums , bass , kick , snare , hi hat , a melody is supposed to be the syrup on the pancake , too much its not good , you need just enough for it to stand out and still compliment the drums . When you find that balance the beat will be " hard "
+ distortion
Yes what both said above, and also, chorus on the melody instruments makes it heavy, and reverb makes it roomy ... with high frequency damping midway high , and decay time also around midway. also eq with 2k and 1k increased a bit maybe also 8k and little bit 16k .
Also panning all the instruments etc properly , and doing sidechain compression with threshold low , and compression ratio 2-4, and little bit of gain and stereo link and detection both on or maybe experiment.
Boomy kicks, open high hats with effects(reverby and flanger for example) , and solid double claps can also do the trick.
closed hi hat and snare with chorus might also help though not tried but reverb and little bit of delay works.
You can also increase the gain in the individual sidechain compressor of the melody to stand out a little bit, but all my advices are after you have made the melody hardstyle I think to fix it where needed..

I do it for my trance music haven't done it much hardstyle that would require distortion , overdrive etc.. Will try it sometime..
chocks
With that i mean abrupt changes! Dont do what seams to be 'natural', and things that 'normally' takes time, do them fast!
HS often has full-span filter-changes over 2-3 beats, where the same in trance, could be over 6 bars.
HS likes to 'play' much more with the sounds that can be made, with any instrument, also those that sounds awful, but done really short, you get this 'chock' i started with.