Hi,
I wasn’t sure it was a dynamic menu you were looking for. I thought it was a link to a specific user.
In this case, you can use the BuddyPress nav menu feature. To do so go into the Appearance > menu page in your WordPress administration. Then create a new menu without assigning it a location.
If the BuddyPress meta box is not displayed on the screen, click on the screen option tab at the top of the page and activate BuddyPress checkbox. You will be able to see the BuddyPress dynamic links menu box. Then add the “rendez-vous” link by activating its checkbox. Save the menu. Finally in the Appearance > Widgets, add a new custom menu widget and select the menu you saved.