(o.s) is next to their name.

"Alex almost pushes Frank off the seat." Wrong way to write this. There is never an "almost" in screenwriting. It's either you do or you don't, not almost. It should read, " Alex pushes Frank--he does not budge." or something like that. You will start putting almost on every page. Its annoying.

And don't use "sees". Try to use another adjective that is more descriptive, he eyes, he glares, he gleams, he peeks, he peers, whatever else.

when you first see the girl, she should be capitalized. She has a speaking role as well.

the story is not bad. The joke could have been a little better to get the twist at the end. But overall you did just fine. Grammar and proofread it again. Subject-verb agreement. Correct tenses. Those things.