How do i ask this girl out?... and fast?

so im at school and its lunch time. so theres like 10 people at my table. and one guy has a cute step sister. so this other guy at my table says "Ima ask her out". and he was saying stuff about what hes gonna do to her and it wasnt so good... he said he's gonna make her a lesbo and take her viginity and all this. and i was kinda mad. and i actually like this girl! and so i want to ask her out before the other guy does! what am i supposed to say to her? and i have to say it quick! because i really really really like her! and i dont want her to get hurt!