It takes two to rules lawyer.

[Khedrac]

The one using tortured logic to justify their position is the rules lawyer, because that's what a rules lawyer is.

I would disagree with this position. The rules laywer is the one who knows (or thinks he knows) the rules well enough to call it when other people deviate from the correct rules, hence player B in this case.
A good rules laywer will try not to interrupt the flow of the game, possibly not saying anything until later, or just murmurring something like "are you sure that is the correct rule?" but will also be ready and willing to respond to any query as to the correct rules.
A bad rules laywer is one who interrupts the flow of the game and argues with the DM halting play.

Good rules laywers can be a real boon to a party as they can be far quicker to ask than referencing the rulebooks for the more obscurely positioned rules.

The players who twist the rules to achieve what they want can be either good or bad rules laywers (or neither), but are probably powergamers.