You have my sympathies. Although it's usually too late, if I realise in time that they are cowards I will pull out ANY stops to beat.
I love this game but sometimes it makes you rage. I went human to fight the gargoyes in NG+, lo and behold some dick invades and runs off like the coward he is to lure me to the balder knights. I stand outside the entrance waiting for him but he circles round the back, (which I am obviously on the lookout for), he then proceeds to BS lag me, not once but 3 times in a row.
The world would be better off without tossers like that, if you're going to invade have the decency to fight fairly and/or honourably. What the hell do they get out of it, fucking twats.