conditional activity page for buddypress [closed]

It sounds like you are using a bp_has_members loop on some page.
I don’t think you can change a define while in a loop.

In that loop, do you have this code?

<a href="https://wordpress.stackexchange.com/questions/226262/<?php bp_member_permalink(); ?>"><?php bp_member_avatar(); ?></a>

And / Or:

<a href="https://wordpress.stackexchange.com/questions/226262/<?php bp_member_permalink(); ?>"><?php bp_member_name(); ?></a>

Then you could do something like this:

<?php if ( bp_get_member_user_id() == bp_loggedin_user_id() ) : ?>

     <a href="https://wordpress.stackexchange.com/questions/226262/<?php bp_member_permalink() ."activity'; ?>"><?php bp_member_name(); ?></a>

<?php else : ?>

     <a href="https://wordpress.stackexchange.com/questions/226262/<?php bp_member_permalink(); ?>"><?php bp_member_name(); ?></a>

<?php endif; ?>