Not sure about U.S. or U.K. arrivals procedure, but in Oz, Canada, NZ the gentleman in the uniform does not just ask you if you have any fruit, he is standing with a signed declaration in his hand in which you said that you had no prohibited items in your luggage, including fruit.
He / she will then ask you whether you understood the form that you signed. Frequently he will have singled you out because you have been profiled; normally by a basset or lab.
And that was just after you had walked past the signs and well-marked disposal bins explaining that carriage of foodstuffs is prohibited.
So, when he pulls an apple from your bag (the "it's just an apple" apple) he will ask you once again whether you understand that carriage of fruit is prohibited.
Remember, he is now holding up at eye level, specifically for you to see, your signed declaration.
He may even explain to you the apple diseases found at your port of departure and not yet found in Oz, Canada, etc. and why carriage of fruit is a) prohibited and b) punishable by law.
At this point, he has decided in his own mind, that you are just plain stupid or being deliberately deceitful (similar to stupid).
Now is your chance to demonstrate that you are not being deceitful and thereby avoid monetary sanction. Just confirm his suspicions.
Admit to gross stupidity, it should be easy for you. Embellish with bizarre (non-threatening) behaviour or statements if you think it will help.
On those grounds, he may just issue you with a warning, written and recorded or just verbal (yes, it does happen).
He has now, already decided your fate. Everything that follows will only exacerbate your position.
You can stand your ground and argue, either politely or otherwise.
You WILL now be issued with an on-the-spot fine, payable immediately.
You can decline to pay the on-the-spot fine, in which case your case will be passed into the judicial system for decision by a judge. You will need a lawyer to have any chance of winning your case.
You could take it to the media which can headline it as "It was only an apple".
Prosecution still have your signed declaration and your apple, in a plastic bag.
Chances of success; not zero but pretty bloody close to it.
So now you have a much enhanced penalty to pay, plus lawyers fees and a criminal conviction (I think, not sure. The judge may strike down the record).
So tell me again, was standing on your dignity really worth it?
After all, "it was just an apple".