I assume it's late at night and almost no one around since you would go full public.
Walk through the park and rub your pussy and clit already while walking. Each 20 steps strip a piece of clothing and leave it behind. Keep on doing this until you are naked (take your valuable stuff and keys though!). Then close your eyes and masturbate until you cum. Then go and collect your clothes again
Please let me know how it went if you did it.