Many of my students stumble over this particular use of the reflexive form which is not academic or formal but, nonetheless, sounds truly Italian.
In Italian we use some verbs which are called ‘Riflessivi’ or ‘Reflexive’ such as, lavarsi (to wash oneself), pettinarsi (to comb oneself), radersi (to shave oneself) and so on. The majority of them are somehow involved with the care of one’s body, for example: mi lavo i denti (I wash my teeth), mi lavo le mani/i capelli (I wash my hands/hair), mi faccio la doccia (I take a shower), mi faccio il bagno (I take a bath). In all these cases the performed action falls on the subject and the listener cannot misunderstand. For example, if I say: ‘Mi lavo le mani’ everyone will understand that I am washing my own hands and no one else’s; but if I say: ‘Lavo le mani’ an Italian listener would be waiting for the name of the person whose hands I am going to wash, for example: ‘Lavo le mani di/a Kevin’.
Sometimes, other verbs can be used in this way, even though they do not become really reflexive, but emphasize that the action greatly pleases or displeases the subject. For example, if I say to you: ‘Questa sera mi mangio una pizza’ or ‘Questa sera mi guardo un film’ or ‘Questa sera mi leggo un libro’, I am already anticipating the pleasure of doing these things. It is almost as if I am going to treat myself. While if I say: ‘Stasera mangio la pizza’ it could mean that I do not have anything to eat and I will have a pizza as a backup or that of the options available, this is the ‘best of a bad lot’.
The trick does not work for all verbs, though. For example, reading the following sentence: il gatto si mangiò il topo (the cat ate the mouse) we can draw the conclusion that he really enjoyed his meal, but we cannot say ‘Il cane si morse il gatto’ as it would not make much sense, besides the fact that he might have bitten himself when he was trying to bite the cat!
To know more about ‘Il cane che morse il gatto che si mangiò il topo’, you can google ‘Alla fiera dell’est’, a great song by the singer-songwriter Angelo Branduardi who also won a price for it in 1978.