This was originally funnier, but only made sense to me. Drew's line in the third panel was more concise, such as "but that really hurt", and Lee's response was essentially the title. The trick of writing humorous gag strips is that you have to meet your reader exactly halfway. If you overexplain the joke, it's not funny. If you force your reader to spend extra effort figuring out the meaning, it's also not funny.
I was thinking about scraping this joke, but I never know which comics will get a positive reaction. Some of my most embarrassingly stupid strips have gotten some pretty good laughs.