Here's an adjustment (re-ordering) of the options you are giving `find`, based on the warning message it is giving. NOTE that I did not get the same warning you are getting, BUT I *was* seeing /proc files/directories in my output when using the command you give there. After this re-ordering, I appear to be getting the right results, but you try it and see.
This would not be the first time that different versions of `find` have acted slightly differently on different systems..
Anyhow, see if this works for you (and if you like, maybe re-combine the -iregex statements into one, but whatever you like..)
find / -type d -regextype posix-extended ! -iregex "/proc.*" ! -iregex "/tmp.*" -perm /o+w
Regards & good luck!