The URL is already rewritten the best it can in regards to Joomlas SEF limitations and requirements. Joomla rewrites them as follows
DOMAIN/ALIAS/VIEW/PARAMETERS
So in CBs case with a menu item you could have the following.
domain/profiles/userprofile/krileon
There's no way to reduce this any further without causing conflicts. If you remove "userprofile" then you are removing the task/view, which CB/Joomla needs to know in order to determine what you're wanting to display.
Having domain/krileon is easy to do on social sites like Facebook, but the environment is designed for it. Joomla on the other hand could have hundreds of extensions, which all have their views/tasks and menu aliases as necessary.
The only way I can think of improving this further is quite significant improvements being done to Joomlas SEF handling. For example URL rebuilding from alias could work and you'd be able to have the below.
domain/profiles/krileon
It'd then take the "profile" alias, match it against its menu alias in the database then reconstruct the request parameters back into the request global. This however is no reliable. For example what if the alias isn't unique? Then this becomes an impossible situation.
Rewriting the URL is actually the easy part, but rebuilding from the rewritten URL in a way that won't conflict with other extensions is where it gets significantly more difficult. Both tasks are done in our router.php.
Now something like the following actually is somewhat doable. However, our URL functions and routing don't account for it.
DOMAIN/ALIAS/USERNAME
This is accomplished by using the following URL structure.
index.php?option=com_comprofiler&user=USER_ID
I've created a feature ticket to look into improving our router further for better looking SEF URLs.
forge.joomlapolis.com/issues/4479