While it might warrant some explaining, dressing as enemies from historical tales could make for some very smart costumes - particularly if your school is able to give prizes to reward the originality of the costumes at a pep rally.
The opening of the movie is a spoof of a long sideline or pep rally cheer - the cheerleaders are doing versions of "roll call cheers", introducing the characters and establishing a haughty sense of pride and entitlement.
While it's in poor taste to 'roast' someone without their knowledge, chances are that for special events like pep rallies, you'd be likely to get some faculty members who are willing to roast themselves in good fun.
Some employers will not mind what color your hair is if your job location is not visible to clients or guests, or a funky hair color might be allowed to show school spirit at a dance or pep rally.
You're about as effective at pep talks as Rhyn.
Is this supposed to be a pep talk?
Gabe turned towards Rhyn, in sore need of a pep talk as only his best friend could provide.
Entertained by her pep talk with the flowers, Deidre reached her towering apartment building a short time later and paused to collect the mail.
"Appreciate the pep talk," Gabe said drily.
To mention examples, blood serum solidified at a suitable temperature is a highly suitable medium, and various media are made with extract of meat as a basis, with the addition of gelatine or agar as solidifying agents and of non-coagulable proteids (commercial " pep tone ") to make up for proteids lost by coagulation in the preparation.