1) Been there, done that 2) Blah 3) Bored exclamation 4) Boring 5) Causing ennui 6) Dull 7) Dull as ditchwater 8) Dullsville 9) Evoking ennui 10) Exclamation denoting boredom 11) Exclamation of ennui 12) Expression of boredom 13) Expression of ennui 14) Hardly engaging 15) Hardly stimulating 16) Indifferent 
Ho-hum is slang for something dull or tedious.
(an exclamation expressing boredom, weariness, or contempt.)