One ESFP whom I was friends with for a while was great despite her many personal faults which were not so much type related. However, she was inclined to jump from relationship to relationship and to be too volatile with her emotions. She could be very affectionate then lash out unexpectedly when in a bad mood which unintentionally caused our friendship to suddenly end (in that I really couldn't trust her and any further attempts to salvage our friendship were failures, sadly.). Was way too impulsive, sometimes violent (even if only to protect loved ones). She was not the typical ESFP but was one nonetheless.
Some ESFPs have proven to be forgetful and unreliable. Of course, I've met more who have been reliable. But usually emotionalism, fickleness, impulsiveness, and lack of personal responsibility would generally be negative traits of the type.