Real Dictionary

ho hum
exclamation: You can say ho hum to show that you accept an unpleasant situation because it is not very serious.
phrase: You can use ho hum when you want to show that you think something is not interesting, remarkable, or surprising in any way.

ho hum in British English
uninteresting; boring; tiresome
used to signify boredom, lack of interest, weariness, etc.
adjective: dull, boring, or routine; so-so
adjective: lacking interest or inspiration; dull; mediocre
exclamation: You can use ho hum when you want to show that you think something is not interesting, remarkable, or surprising in any way.
interjection: (an exclamation expressing boredom, weariness, or contempt)