Similar happened to me, and the following then occurred.
1) Kid with his mum, throws half his icecream wrapper on the street as she is loading up her shopping. It was a cornetto, and he just ripped off the top half and dumped it on the floor whilst keeping the other half wrapped round his cornetto (if you get me).
2) I say to mum 'I'll pick this up then for him shall I?'
3) I pick up half the ice cream wrapper and have it in my hand and move towards the bin
4) Mum says 'He didn't drop it someone else did, don't make stuff up'
5) I say 'well, yes he did drop it' and start walking away
6) She says 'No he didn't I was watching him the whole time (voice raising now) who are you? who do you think you are?'
7) I say 'Listen, Yes he did. I'll put it in the bin.' I AGAIN start walking away.
8) She runs up to me and loudly says 'Listen he definately didn't - who the **** do you think you are, it's DEFINATELY not his, I was watching him the whole time, I promise you he didn't you ****. Who the **** do you think you are? Lying about my little boy? You ******* ****. You ******* **** *******!!'
9) I say 'You're mistaken, he dropped it'
10) Her 'NOT A CHANCE - He didn't, I WAS WATCHING HIM, HE DIDN'T. whats your ******* problem?'
11) Me 'You're mistaken or lying then, he did. And I can prove it'
12) Her 'What?'
13) Me 'I can prove it's his. Look, here is the half of the cornetto wrapper he chucked - match the 'tear' up against the bit he still has in his hand'
14) Her .. 'Er .. what? What? No. **** off. He did NOT drop that litter.'
15) Me 'Just match it up .. I can easily prove you're lying or mistaken. Your kid (who was protesting his innocence throughout' is DEFINATELY a liar. I can prove he dropped it .. just match up where he teared this bit off, it will match.'
16) Her 'No. You are a ******* ****, I'm not doing that - I am not lying you are lying .. I'm going to call my husband to come down here and beat you up. Don't lie mabout a 12 year old kid. What kind of sick **** are you?'
17) Me 'You're going to call your husband to duff me up? I don't believe you, as I know you lie'
18) Her 'I'm not lying, I'M NOT LYING'
19) Me 'I don't believe you, as I know you lie. You're a proven liar.'
20) Her 'I'm calling the POLICE. YOU ****. I'M CALLING THE POLICE.
21) Me 'I don't believe you, as you're a proven liar'
22) Her 'I'm 43, and I've never met a bigger ******* than you.'
23) Me 'I don't believe you, as you're a proven liar'
24) She changes into her huge landrover, for some reason really over-revving it as she skids away, as it that would 'teach me' somehow.
Think I made her day slightly worse, which is justice for her littering, and restored balance to the yin/yang of the universe!!
