Solo dining

Please tell me that this has happened to every couple who ever ate out in a restaurant.  Your partner goes to the toilet and the next moment the food arrives.  What do you do, start eating or wait until your partner returns?  If you do wait, for how long?  Are there no limits?  Larry David would know what to do.  Me, I try to nibble inconspicuously so that no-one else in the restaurant can tell I'm eating alone, and so that my wife won't know I've started when she comes back to the table.