250 jumping jacks in my briefs for frat initiation--will I get an ?

I am worried that I'll get an , especially if my rubs against the fabric in my briefs and bounces up and down during the 250 jumping jacks. What are the odds of an involuntary and will it be super humiliating?? Will the constant stimulation and friction on my ' head be painful or unpleasant? I hope that at least I won't . God, this is a nightmare.