He will tease you or do nice things for you when asked. For example, if you ask him to bring your chair over, he might do it. He also might try to show off by telling her about his accomplishments in sports, school, etc. He could act really nervous around her, like if he can't look at you for a long time. He doesn't have to act all these ways if he likes you. It really depends on the boy.
Dear random confused girl
Here is a small thingy advise
If he looks real good in some clothes tell him cause he might change to those clothes so you think he looks nice
In groups he wil try not to look derectly at you or if he does he looks at the ground next.
hope this helps
Good luck your friend