Demean yourself like this. Make it sound jealous, sexually frustrated, and desperate.
Say:
"It's not fair. He probably has sex all the time, while I sit at home, tugging my tiny dick."
"I bet he can give girls the wildest nights with his big thing."
Maybe you can use your hands to represent his size. And watch her expression change.
"I felt so scared around him."
"Even the veins on his dick were fearsome."
"He's so much taller than me, despite being younger."
"I think I flinched a little when I heard his deep voice."
"Is it normal to be submissive around a guy like that?"