A guest was hurt in my party. I paid his medical bill. Is this expense deductible in the U.S.? If so, where does it go on 1040 Schedule A?
No, unless the guest is your spouse or dependent. From the IRS:
If you itemize your deductions for a taxable year on Form 1040, Schedule A (PDF), Itemized Deductions, you may be able to deduct expenses you paid that year for medical and dental care for yourself, your spouse, and your dependents.