Sneakily

Ziri sneakily approached the house.

Mark tried to sneakily watch Jessica.

Robert found Sandra sneakily using his laptop.

Yuri sneakily took some photos of Martha.

I sneakily approached the house.

But on the occasions that he did do something actively nasty, he was satanically good at insinuating himself so sneakily into your most sensitive spots that if you did not know him well you could end up thinking you were being unfair to him when he annoyed you.