This guy I've recently started playing with uses Hellish Rebuke, then on his next round he uses his pact blade to "cut himself for 1 point of damage" as a minor action. He claims this triggers Hellish Rebuke, as the text reads "if you take damage before the end of your next turn, the target takes another 1d6+Con mod damage." Does this fall into the bag 'o' rats section of rules or is there something that prevents this? Just seems pretty ridiculous to me.