if an event is in full swing, it has already been happening for a period of time and there is a lot of activity.

When we got to Vicki's place the party was in full swing.

• be out on the tiles
• be out on the town
• be out on your ear
• be out to lunch
• be over and done with
• be over the hill
• be over the hump
• be over the moon
• be over the top
• be own flesh and blood
• be own man
• be own master
• be own person
• be own woman
• be own worst enemy
• be packed like sardines
• be par for the course
• be part of life's rich pageant
• be part of life's rich tapestry
• be part of the furniture
• be past it
• be past sell-by date
• be past your sell-by date
• be penny-wise and pound-foolish
• be pie-eyed