well it's a public place and everyone is at liberty to sit
anywhere they want but normally, u cant be shooing them when they
are carrying their tray and asking politely if they could share a
table.. Sometimes, i do that and sometimes, i got people doing that
to me..and it will normally be a cuppa if i'm sharing tables with
people...It all starts with a smile 
Yea...maybe because I have this mindset that once I am sitting
at this table, it is off-course to the rest.
Yes, it is a bad mindset I know, one which can only be
maintained in a country with little to no visible human
traffic.
But sumtimes if I am eating out with a number of people and
suddenly a stranger wants to join us I will feel bad for him or
her...cos we will be talking away and making a lot of noise then
the poor girl or guy like so isolated...