How to purposely ignore and avoid someone during gym class?

Short story is my little sister use to have a crush on him last year now he’s in her gym class and she avoids and ignores him the best she can, (he has a huge asshole to her when she liked him)

But sometimes she can’t help but look at her to see if he’s looking at her still, she doesn’t want him to think she’s still interested. She said he looks at her sometimes still and it’s only been the second day.

She wants to know how to purposely make it so obvious that he knows she doesn’t like him at all and is purposely trying to avoid him and ignore his presence? Any tips?
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She’s in high school
How to purposely ignore and avoid someone during gym class?
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