Pressing you buttons is an expression in English, we usually use it when we know a person quite well. If you are familiar with someone and get to know their temperament either you or they will know how to irritate or upset them. For instance if you know that Felicity is on a diet, you could 'press her buttons' (upset her) by giving her some chocolate!

If a person knows how to make you react negatively to them or something they do, they know how to push or press your buttons.

The reason it is called pressing buttons is because a person can manipulate you as though they no where your controls are... To map you mad- I press this (do or say this) To make you happy I press this (do or say this) to get what I want I press this (do or say this). They control you like a machine. The phrase is used for making a person mad on purpose though -

It is an expression meaning that you are irritating someone. You are metaphorically pushing the buttons that set them off.

To press someone's buttons means to irritate them or get on their nerves. When you get to know someone well, it can become easy to irritate them because you've learned which buttons to push.