Izuku smokes.

When the challanges of life get the better of him,the pain is too much and he becomes numb. A feeling of doom and hopelessness churns in his stomach, and to distract himself from that pain, he smokes to 'relax'.

Izuku gets a message on his phone from Katsuki. Katsuki messaged that he's coming to his dorm to cuddle.

But Izuku doesn't bother reading it, and continues on his second drag,letting the smoke stay in his lungs for a moment before exhaling it through his nose.