Which word or word phrase most clearly has a negative connotation Irresponsible Nonchalant Aloof Carefree?

The Word "Irresponsible" most clearly has a negative connotation, as it implies a lack of accountability or reliability. While "Nonchalant," "Aloof," and "Carefree" can have neutral or even positive aspects, "Irresponsible" suggests a failure to meet obligations or duties, which is generally viewed unfavorably.