I a bit less of an A-hole online than I am in my day to day activities.
For example, I held the door to a 7-11 open for this woman, she just breezed on in, not a thank you, not even a look in my direction, not even acknowledging my presence.
I calmly let the door close and said "You're welcome you ungrateful fat cow."
She turned and got all huffy and said "What did you say?"
My reply went something like this "When someone does something nice, its common courtesy to thank them, even in a small way. However, since you seem to have no common courtesy for others, then you deserve none from me."