Top 10 subtle hints your flight will be delayed
 

I'll start:

--Cabin crew is instructed to serve food and drink while still on the tarmac
--Both pilots walk off the plane right as boarding commences
--3 syllables: DE ICE ING

Top 10 subtle hints your flight will be delayed
 

-- No airplane at gate
-- Mechanic on a tall ladder is opening up side of engine.
-- Air conditioning does not work (on some planes air conditioning and pressurization are handled by the same system)

You get a notification from FlightTrack or see it in Flightaware before it's announced by the pilot.
You see the incoming flight is delayed.

Top 10 subtle hints your flight will be delayed
 

You're flying American Eagle on an ERJ or CR2

Top 10 subtle hints your flight will be delayed
 

Everyone rushes to the window as smoke billows out of the right engine on the Q400.

Top 10 subtle hints your flight will be delayed
 

They've just announced your aircraft has arrived at the gate, and will ready for boarding soon. . . . . but you can't see it out of the window because of the blizzard.

Anything the captain says that begins with "Well, folks...".

when you see the flight crew in a fist fight, seems to happen more frequently in recent years

Boarding time came and still no bird--and yet they were insisting it was on time.

(And I cracked up a deadheading crew by saying the plane really was there--it was just a stealth plane, we couldn't see it. After all, it was going to Las Vegas.)

It's an hour before departure, flight status shows "on time" departure, but inbound flight status shows "late arrival", currently estimated to be 10 minutes before your scheduled departure.

You're on a United flight

Macadamia nuts served in bags!
 

Improperly served Macadamia Nuts

You're seated in the plane, look out the window, and see 5 guys staring up at the wing with a giant flashlight.

There's an announcement requesting volunteers to help push the plane.

Top 10 subtle hints your flight will be delayed
 

The flight attendant ask over the PA system if anyone is familiar with piloting the plane