Is there a song which cannot be made funnier by dropping the word "Trousers" in there somewhere...

I think the real key here is that the word "trousers" is unexpected at all moments, so find songs with the word "pants" casually thrown in and exchange it for "trousers". Sort of like those coffee commercials, except instead of a rousing new coffee taste that startles yuppies into confusion, it inspires helpless laughter.

'dropping' the word 'trousers' ...?

Lots of girls and lots of boys
Lots of smells and lots of noise
Playing football in the park
Kicking Pushbikes after dark
Baggy pants, dirty shirt
Pulling hair and eating dirt
Teacher comes to break it up
Back of the 'ead with a plastic cup.

Oh what fun we had
But, did it really turn out bad
All I learnt at school
Was how to bend not break the rules
Oh what fun we had
But at the time it seemed so bad
Trying different ways
To make a difference to the days.

Baggy pants, baggy pants, baggy pants
Baggy pants, baggy pants, baggy pants

Dry your trousers mate.

LMLYT

The Man Whose Trousers Expanded

Ain't no trousers high enough...ain't no trousers low enough...ain't no trousers wide enough...to keep me from gettin' to you, babe.

Smells Like Teen Trousers

"If you're having trousers problems I feel bad for you son..."

The Du:

Celebrated Trousers
Broken Home, Broken Trousers
59 Times the Trousers
Trousers I Make
Terms of Psychic Trousers
Hate Paper Trousers
Trousers Somehow
Hardly Getting Over Trousers
Dead Set on Trousers
No Trousers Have I Made
All This I've Done for Trousers
These Important Trousers
Charity, Chastity, Prudence & Trousers
Standing in the Trousers
Ice Cold Trousers
Trousers in the Air
Trousers Control
From the Trousers
Trousers Drunk
Flip Your Trousers
New Trousers Rising
Trousers, You've Got to Fall

You forgot "Books About Trousers" and "Don't Wanna Know If You Are Trousers"

"Promises me I'm as safe as houses,
as long I remember who's wearing the trousers."

Wait, maybe I misunderstood the question.

Here's one I heard on the way to work this morning:

The Animals - House of the Rising Trousers.

Kraftwerk:

Trouser Counter
The Trousers of Energy
Hall of Trousers
Showroom Trousers
Metal On Trousers
Endless Trousers
We Are the Trousers
Neon Trousers
The Trouser-Machine
Boing Boom Trousers
Trousers Non-Stop
T(r)ou(se)r de France

Fahrn Fahrn Fahrn auf den Trouser Barn

Belle and Sebastian:

Your Trouser's Blown
If You Find Yourself Caught In Trousers
Judy and the Dream of Trousers
Step Into My Trousers, Baby
A Century of Trousers
Could Have Been Brilliant Trousers
Stay Loose, Trousers
The Boy With the Arab Trousers
The Trousers I Am In

Oh, why not...Radiohead:

I Might Be Trousers
2+2=Trousers
Sail to the Trousers *or* Trousers to the Moon (I can't decide)
(Nice Trousers)
etc.

"Promises me I'm a safe as houses, as long as I remember who's wearing the trousers..."

Oh wait, that WAS the lyric!

"What have they done to the Trousers?" (The Searchers)

donald where's your trousers

Journey!

"So now I cooome to yooou with open trousers - nothing to hide, believe what I say. So here I am with open trousers - hoping you'll see what your love means to me. Open trousers."

Honorable Mention
Three Corduroys and the Truth - U2