I think David is just sick of Priya always correcting everything he says, and it comes across as a lecture, nitpicking or a dig at him. It sounds like she starts a lot of private discussions with David as well, and he probably feeling like she's becoming a nag. He probably understand were she's coming from at times, as he's said he does say stupid stuff at times but he wants her to treat him like an equal, not talk down to him.
We've seen Priya say she's trying to cause a wedge between the guys, and after Tom and Richard leave this week, Ryan and David will be put under more pressure from the other group..
Priya did it to Sandra as well after Sam left (we saw her talking about it in the kitchen), and even Sandra told David at the BBQ she felt on the outer now
HM's can insinuate that David threw Ryan under the bus at nominations but David can't defend himself because of the rules. Ryan never had the dirty dozen power to know what happens.
I don't think Ryan would have voted David 2 points to be HOH again if he thought he was out to get him..