Green’s Dictionary of Slang

1. to be incompetent.

1719		in D’Urfey Pills to Purge Melancholy V 340: Still hawking, still baulking, You flash in the pan.
1840		R. Barham ‘The Smuggler’s Leap’ in Ingoldsby Legends (1842) 165: But his second horse-pistol flashed in the pan!

2. to have sex without ejaculation.

c.1720		‘Original Black Joke. Sent from Dublin’ 🎵 His main spring it was not strong / For he could only flash in the pan.
1848		Boston Blade 10 June n.p.: But being exhausted, his gun-lock was poor, / He flashed in the pan, and fell on the floor.
1865		‘Rory O’More Had A Hell Of A Bore’ in Rambler’s Flash Songster 12: I’m the boy your touch holes to prime; / I never miss fire, or flush in the pan, / When I go shooting it is not my plan.