How to debate hypothetical vegans

Earlier today, down at the shops, just as I was simultaneously buying an ice cream (Cornetto, thanks for asking) and planning a daredevil escape from the environmentalists walking up and down the street carrying clipboards (crossing the road while they were looking the other way), a devious plan struck me.

The plan was this: I would buy one of the environmentalists - an ice cream.

No no, hear me out! The conversation, as I imagined it in my head, would take place something like this:

ENVIRONMENTALIST: Hi, can I speak to you for just a min.... 

TIM: Would you like an ice cream? 

A devastating counter-attack, I think you'll agree. Of course, being environmentalists, I realised as I thought about this stratagem, they would probably have to say...

ENVIRONMENTALIST: Oh no thanks, I'm vegan. But how lovely of you to ask! 

TIM: OH WELL I WILL HAVE TO HAVE IT FOR MYSELF THEN HOW SAD*. 

Brilliant, c'est non? But things were about to get very hairy, I realised, in this hypothetical situation:

ENVIRONMENTALIST: Great anyway so on this pamphlet I have here....

But don't worry! My defence is rock solid!

TIM: Mm mmm MMMM THIS ICE CREAM IS SO GOOD! YOU WOULD LOVE IT IF YOU WERE ALLOWED TO HAVE ANY OF IT! OH MY! MMMMM! 

But then, as I was thinking about this pleasing scenario, it suddenly struck me that maybe my planning and scheming was all wrong. What if the environmentalist actually did want the ice cream? And stood there - eating it - in front of me?** True - they wouldn't be able to talk to me anymore about whatever it is they were talking about. But they would be eating my ice cream!

Outwitted by hypothetical non-vegan environmentalists. Well, that was a first.

So in the end I just bought one fucking ice cream and nicked across the fucking road while they were looking the other way.

*cf Psalm 23, v. 5: "Thou preparedest a table before me in the presence of mine enemies.... my cup runneth over". 
**Psalm 23, v. 5 again!