I heard this one in a documentary about foot fetish.
The woman who produces fetish videos says:
A lot men like feet. But you can only do so many of them.
What does this mean? I googled but couldn't find any idiom like this. I found however similar usages, like:
"You can only do so many bar crawls. Get some culture into your life,..." "You can only do so many tasks at one time, so it makes sense to focus in on what is really required." "You can only do so many movies in a certain time, so I've acted outside of those ones too. So, it wasn't really that big of a thing."