Why would a guy call himself a jerk?

Cuz he knows he is

No self respect?

maybe he is being honest

Usually because he wants you to tell him he’s not..

Honesty. I've called myself much worse and yet people still have outrageous expectations of me.

It makes sense in the context of an apology or self honesty about messing up sometimes.

To make you feel compassion towards him

Self-recognition?

Maybe jerking is his favorite pastime.

Well, he knows himself best, I suppose. Or he’s being extremely self-effacing.

I always call myself that when I screw up. 😁

No longer in denial.

I am not a "jerk" but have done stupid things in the past and apologized for being a "jerk" at that time 🤔

He's a simp.

Jerking off

Clean out your ears, he was telling you he just finished a jerk