Here is a story:
The first or second time i rode more than fifty miles on my bike on a hot summer day I thought it be a good idea to take a break and get a banana milkshake, so I rode around fifty miles and had my fill; however, i still had a good twenty or so miles back to my house. I was parched, looking forward to that nice cold creamy reward for getting through the hard part of the ride. I was in my glory drinking that milkshake on that hot day.
It then was time to head out and back home. At first I was feeling alright, and wham... five miles from that tasty treat my stomach started to hurt my legs became lead the sun felt fifty degrees warmer and I started sweating custard. I think I averaged around 10mph on the ride back and was in agony the entire time. I have never cursed ice cream before but on that ride I SCREAM, and screamed a lot!
So, in short, milkshakes are a NO GO pre or mid ride. A nice chocolate milk post ride however, Gods glory!