Making fun of EX GIRLFRIEND?

Why would a guy make fun of his ex girlfriend to his new girlfriend? Why does he even care what he's ex girlfriend is doing? :')
I don''t understand when they both find it amusing making fun of the guys ex girlfriend and stalking her to see her reaction, especially the ex girlfriend he was meant to marry? Why would a guy do this with his new girl?
Making fun of EX GIRLFRIEND?
Add Opinion