Is it normal that i found this so hilarious?

On June 19 2010 I had a friend over and we were making spiders. (fizzy cordial and ice cream) like we always do. when my sister drank some of hers, she screwed up her face and yelled "it tastes like soap!" and I laughed so hard I nearly wet my pants and had to run straight to the toilet. When I came back I was still shrieking with laughter. My friend said I looked like I was going to explode and that she'd never seen anyone laugh so hard in her whole life. We still of course bring this up all the time and laugh about it. Is this normal or have I gone mental?