Please, can I corporally punish just ONE?

Some strange process seems to take place in my brain whenever a slip comes home for a field trip or a class event asking for parent volunteers. I don't really know why. Generally I like to think I'm fairly clear-headed as far as self-knowledge goes. I don't buy clothes that are too small thinking I'll lose weight and fit into them. I don't invite more people over for dinner than I can comfortably cook for. I don't buy a bag of cookies unless I'm prepared to personally eat every single one, should it be required of me.
So what is it about those pink or green slips of paper that suddenly renders me incapable of remembering that I am a grumpy, unpleasant person who doesn't like noise, or crowds, or children (apart from a fairly narrow selection)? No, now I'm suffused with visions of myself as a serene and patient dispenser of knowledge and guidance, surrounded by sweet, laughing children looking up at me worshipfully (I know -- I have got to check what the hell they're mixing in with the toner).
Oh, did I mention that I have a Master's in Comparative Literature? Therefore, I am uniquely qualified for.. well, sweet fuck all, if we're being brutally honest. Certainly not for something called "Scientists in the Schools". The other two times I volunteered for Scientists in the Schools it was for Junior and Senior Kindergarten, and it didn't involve much more than making playdough bugs and trying to teach four and five year olds how to say 'proboscis'.
Angus is in grade three now, and this one was about forces. So whatever... gravity, friction, inertia, light sabres. One adorable little girl watched me fire up the gyroscope and said "it's like magic!" and I was like "yes! Magic! Wait, no -- it's physics!" Apparently it's not acceptable, either, to say "Excuse me, this group of kids is kind of dumb and they won't stop touching the salad spinner; can I have a different one, please?" Smacking hands is frowned on, also, which is bogus because man, don't some hands just cry out for smacking? Not to mention the fact that Angus looked half-dead and couldn't stop yawning (too much Diary of a Wimpy Kid last night, I guess). When the teacher said thank-you, I'm pretty sure she meant for leaving and never coming back.
On the up-side, it's Friday, and now I feel really entitled to my nudity, sexuality, violence and coarse language.