Some guy keeps messaging me, telling me about how bad i am. Is there any way to block someone from messaging you?

report that player to mods.

It isn't against the rules to message someone telling them that they suck. Reporting them to the mods will not do anything except annoy the mods.

Just don't respond and ignore him.

In my experience, people who talk/act like that usually aren't very good themselves. It's like saying "I'm a slightly less sucky newbie than you!" Your response should be to start following a legit strategy to grow faster and then let your actions speak for you when you pass and landgrab the idiot.

most likely just a player named JayR looking for more trolls

Most noobs just forget to buy enough tech, its like going to the supermarket in your underwear, hoyo.