Oh lawdy... I lol'd xD
I'm not 100% convinced this would be such a good idea myself, since comments are there for a reason. If I wanted to hide them, I wouldn't have put them there in the first place... having said that, if other people can see a use in it, then why not?
I would suggest something along what deadeye was thinking, like a little icon that appears at the top of the event sheet or something which indicates comments are toggled on/off. I guess while you are at it, you could make one for groups as well?
Also, being able to group comments together and collapse them, would be handy without having to use an actual group. don't know if this is possible, but I could certainly find a use for this if it were a feature.