If you are sexually active, by that i mean have sex with others, then you must get evaluated by a dermatologist and see what the bump is about. Usually the groin area has some glands called lymph nodes which can get enlarged due to many reasons like injury to legs or feet, infections in urine, etc If you are NOT having sex with anyone, the bump could be harmless, but nevertheless it must be shown to a doctor. There are many conditions where such bumps may reveal a hidden disease like tuberculosis or other conditions.