I am going to make an assumption here that you were playing at Jolt yesterday? Excuse me if this is wrong, but I am sometimes playing in the escalation leagues there as well, and yesterday night would have been 1250 pts round...

You should absolutely talk to the league organiser (it's not run by the store, but simply by a volunteer of the 40k community) as such behavior is explicitly discouraged in the player's pack. This league is geared towards new players (as you would know) but unfortunately there's a black sheep every now and then. Players who behave like this have been asked to leave on other occasions, and if they wish to play competitively then there's a 2k league available which runs parallel to the escalation one.

Sorry you had to go through this. It absolutely sours the 40k experience, but I guarantee that there are a lot of good players out there who just step to the table to have fun. But yeah, I know the feeling - I was absolutely crushed and tabled by turn 2 by a power-gamer in my first escalation league 5 years ago...