If someone is already using the venue, I personally think the done thing is to speak to them first, and maybe ask if they can incorporate your wishes in an event (or work together at least) It isn't a matter of being a baby, it is a matter of respect (and I don't mean in a contrived way) I have had this situation many times over the years, and it just so happens, the said peope have approached me before the venue because they were aware it was the venue I use, and every time, I returned that respect (consideration more so) by working together, and helping as much as I could.
There's more to it than 'throwing ones dummy out'
No offence intended - That is the way I see it, and best of luck with your event mate. If what I say happens to make you have a rethink and you approach the said promoter with this in mind, I bet you they will do everything they can to help you - It's so much nicer
All the best,
Len
P.s - Also good luck with raising money for Charity (obviously), but that doesn't make any difference to how I think things should be approached
P.p.s - It's a shame the person in question was rude to you, as you seem like the kind of person who would understand his objections, if spoken to properly, and no doubt would have sorted something amicably there and then - Good luck mate