The dark side of love theme.
Make the environment tantalizing but sinister.
Each character is hears 'whispered, sweet nothings' in their ears.
The disembodied voices try to seduce and tempt. Play it up.
As they get nearer to their objective, the whispering becomes suggestions (as in the spell) with a increasingly difficult DC as the party proceeds deeper. The suggestions are to give themselves over to their base desires.
Suggestions are to perform self gratification on themselves, or to hit on other party members or near by demons, or to forcefully 'take' another individual, to make 'love' to some nearby beast or monster.
Getting a hard-on while in full plate armor due to a failed save could be problematic while amusing. And can take on a serious tone when as a side effect of the failed suggestion, the demonic environment cause a real or an illusionary resizing in the the individual's external sex organs. Male party members with penis three or four times their normal size.
Imagine a fighter tearing off his armor to perform self gratification, particularly at a very inopportune time (like combat).
Hopefully, I have not been too graphical or too over the top with this
For inspiration, you can rent 'Flesh Gordon' and its sequel. Its campy, corny, low-brow and definately a 'D' movie, but it deals with almost the exact subject matter you are looking for inspiration on.
