With friends like that, who needs enemies.
I too have pulled some pranks on friends (and family) over the years, but nothing that caused physical pain.
One of my good friends growing up was afraid of clowns. Senior Year of HS in 91 a bunch of us go to a very good haunted house in Romulus. I step out of line to "get a pop". I walk up to the head of the line and ask the guy a favor. "Do you have a clown in there?" He replies "Yeah, we do actually." "Ok, try to remember me and we'll be up in about 30 minutes, I'll nod and you make the call. My buddy will more than likely be in the back of our group. He's afraid of clowns."
We go up, I nod, my man uses the radio. We get about 1/2 way through and I see the clown up ahead. I pass him and let im know where my buddy is. I turn around to see this idiot grab my buddy and then scare him. My buddy let out the loudest "Holy S***!!!" I've ever heard and knocked the clown with a single punch.

I wanted to laugh my collective arse off at the time, but I felt bad for the clown. Then after playing back what I saw, he shouldn't have touched anyone. So, I laughed the lightest of the group (which is still pretty good). A lot of what made it funny was the "I don't believe what I just witnessed factor".
When I see him to this day, he gives me hell for "scaring me", but even said, "If the shoe was on the other foot Jay, I'd do the same to you in a heartbeat. I know you didn't mean for that to happen, you're always trying to make others laugh."