Laughing so hard that it causes tears to come out of your eyes is not an easy thing to happen. It has happened to me a few times and always with very good friends with a lot of confidence between each other. I will share the last time it happened which now that I think about it, was like 6 years ago :O
Well, we were in a mandatory basic computer class and I went next to the teacher because she was explaining something to some girls. When I saw what he was doing I wanted to die, he wasn't explaining anything complex but just showing them how to leave comments on a blog. I suppose the girls weren't used to explore the internet but I really don't know. The thing that made us laugh was the following.
While the teacher was talking to them, he wrote his comment and when he wanted to publish it the website requested a captcha but he didn't notice it, so he was hitting enter/publish button and the message didn't go through and he started to become frustrated and sort of agitating his hands because he couldn't accomplish what he was trying to show the group of female students. His reaction when realizing his message wasn't being published was something like this:
He did something like that several times and well... I quickly went to tell my friend and he started to laugh uncontrollably which made me laugh uncontrollably as well and that went on for the rest of the class. I admit we were a little bit immature but laughing so much that tears come out of your face is always worth it.