1) Completely joyless 2) Dull 3) Dullsville 4) Far from enjoyable 5) Far from pleasant 6) Gravely serious 7) Hardly enjoyable 8) Like a buzzkill 9) Like a toothache 10) Like party poopers 11) Not at all exciting 12) Party-pooperish 13) Quite a drag 14) Too Puritan 15) Too serious 16) Zero laughs 
NOFUN is military slang for No First Use Of Nuclear Weapons