I'm going to call a girl out in front of the whole class for bleeding through her white pants
Why would you call this girl out?
She reminds me of someone who cheated on me once, I want revenge.
Don't you think it will be upsetting to the girl to embarrass her like that? I'm sure you'd be upset if someone did this to you. Besides, even if she looks like your ex, she has nothing to do with her at all.
It's my business so nobody can question me. Besides I am the winner, she will thank me for calling her out and humiliating her.
If you want her to thank you, then why not pull her aside quietly and let her know so that she can take care of it without any embarrassment.