Not necessarily worst, but general poor behavior, in lounges and in other public spaces in general:

* Feet on table, other chair/furniture. Bonus: bare feet!

* Hogging multiple seats with belongings

* Leaving large mess behind

* Loud phone calls

* Open broadcast of music/media (and kids with games)



Personal pet peeve: in lounges where there obviously is no wait-service, bossing the staff as if they were personal attendants! ("Can you bring me 2 glasses of OJ with a scotch, and a bag of chips....")