All dictionary references from CHAMBERS ONLINE
untrue adj 1 not true. 2 not accurate. 3 unfaithful.
The lyrics were initially based upon the word “bad”
bad adj (worse, worst; slang badder, baddest) 1 not good. 2 wicked; immoral. 3 naughty. 4 (bad at something) not skilled or clever (at some activity). 5 (bad for someone) harmful to them. 6 unpleasant; unwelcome. 7 rotten; decayed. 8 serious; severe • a bad cold. 9 unhealthy; injured; painful • a bad leg. 10 sorry, upset or ashamed • feel bad about what happened. 11 not valid; worthless • a bad cheque. 12 slang very good.
Especially the contradictory definitions 1 (not good) 5 (harmful) and 2 (wicked; immoral) and 12 (very good). This contradiction led to the title Untrue.
The story the verse lyrics ostensibly purport is a narrative of various unpleasant events and undesirable situations:
A lethal poison in my body.
A virus … a cancer … a disease in my lungs.
A sickness … high fever … insomnia.
The chorus reiterates the word bad which, in the sense of the apparent narrative, is construed to mean not good / harmful.
The word Untrue can be construed in the (slang) sense of the word “not true / unbelievable”. As in “I can’t believe (this nightmare) is happening to me.”
The word Untrue is also the key (as in unlock) word, implying there is more to the lyrics if they are construed as being not true / their oppostite.
The hidden song narrative is the exact opposite and is about the feelings and emotions caused by the love-affair with/lust-after a really desirable woman.
A lethal Poison refers to the Alice Cooper song (both it being about heroin, (in the bad=bad sense of this song), and about trying to resist the temptation of a really desirable woman, (in the bad=good sense of this song).
Like a virus – virus noun 4 anything that … corrupts.
Infectious – infectious adj 3 said of an emotion, opinion, etc: likely to be passed on to others • Her laughter is very infectious.
Like a cancer – you’re eating me up. – she’s constantly/preying on my mind.
It’s so bad I’m delirious. It’s so good I’m delirious adj 2 very excited or happy.
Like a night – of hard drinking. Like a day – on cocaine. (Not necessarily bad things per se).
A silver bullet – a supposed solution to a/all/many problem(s).
Like a disease – gone airborne, in my lungs – I breathe you in.
– infatuated – see “Breathe You In” (Track #7) on the album Home.
It’s a sickness – consuming me, – an addiction.
in my blood – delirium – see Poison / Delirious references above.
Another night – I’m holdin’ on tight. (hold on tight – try to win / continue in danger)
Beyond things – I could dream of. – exceed my wildest dreams/fantasies.
You’re the splinter in my brain. – the thing I always think about.
A high fever – Peggy Lee song (Fever) reference.
– I’m burnin’ up, – heavy desire for someone (Jonas Brothers song (burning up) reference)
trembling about to cry your name – on the point of an orgasm.
You’re so bad, but you’re so good, – wicked/immoral – sexy/horny
a wild thing, that can’t be tamed. sexual inference – good/dirty and insatiable in bed.
Another night – insomnia. No sleep due to all-night sex.
Another day – thinking ’bout you. Infatuation.
My doctor says – I’m incurable.
Got me thinking – it could be true. – I’m in love/lust.
The chorus reiterates the word bad which, in the sense of the hidden narrative, is construed to mean really good / very sexy. The word Untrue can be construed in the (slang) sense of the word “not true / unbelievable”. As in “I can’t believe she’s happening to me.”.
Furthermore the lyrics could be interpreted as a love affair with a married woman. The verses narrating a story of how “bad” the woman is, and the “untrue” of the verse referring to her unfaithfulness.