I'm thinking about grabbing this girl's shoulder. What do you think?
Why do you want to grab her shoulder?
She's always boasting about herself and I can't take it anymore
If she doesn't want to be grabbed you shouldn't do that. You need to have more respect for her space and privacy.
I'll say it's all a misunderstanding.
But it's not a misunderstanding if you're thinking about doing it beforehand. You shouldn't go along with this if you know it would lead to an argument.