There is no "Hide Items not involving me" button for the "All Expenses" tab. It is there for the specific groups.
I also tried to go to the group that I want to hide transactions from and then come back to the "All Expenses" tab, but it does not seem to work.
It would be good to have this functionality since I need to track transactions, and not just what I owe most of the time, and the alternative, "Recent Activity" tab does not seem to be of the same use. Don't know how difficult it would be to implement this for the Web App, but it certainly would be good to have this option since it reduces clutter from groups that I am not usually involved in.