I can't think of a way to have explicit recognition of events without creating and tracking flags, but implicit recognition is possible via a rumour system. I don't remember Newlife's variable names off-hand, so they'll be generic here. Taking a stub form of the custom scene idea you suggest as an example:
At her house, your friend [Amanda] introduces you to her new boyfriend. It's [Joe], your jerk ex.
Joe is a jerk to the PC in the scene and the PC decides to leave.
- You're too shy to explain anything. You stutter a feeble excuse and leave immediately.
At this point the game logs a RUMOUR about you by Amanda, noting location, time, attendees, type (RUDENESS), and temporary penalties on Amanda's TRUST and ADMIRATION for you. In this example, when the next friendship / house party event happens, the temporary penalties cause the PC to fail these checks and she ignores your invitation (isn't added to the list of potential participants). As weeks tick by without contact, her TRUST, ADMIRATION and LOVE for you decay gradually until the game triggers a friendship end event and refers to the most salient RUMOUR in Amanda's possession:
You're distracted by a quiet but angry voice coming from your pocket. You're surprised to find you've butt-dialed [Amanda]. She doesn't know who's at the other end of the line and is threatening to call the police on the silent stalker. You realise your old friend has deleted your number.
- You timidly identify yourself but it does little to appease her anger. Of course she deleted you! She still hasn't forgotten [how rude you were] [at her house] [two months ago].
- In the safety of your home, you finally pluck up the courage to explain. Over the next couple of hours you find yourself telling her everything that ever happened between you and [Joe].
At this point the game marks the RUDENESS RUMOUR and its penalties as invalid, and converts its entire log of events between the PC and Joe to a series of new RUMOURs. The effects on Amanda's TRUST and ADMIRATION for Joe and the PC will be personality-dependent.
[Amanda] is quiet for a long time. Finally, she tells you it's a lot to process and hangs up.
Next week, [Amanda] calls to say she's sorry. She's not sure she's ready to believe everything you said about [Joe], but she hopes you can be friends again.
The immediate consequences of the custom scene end with appropriate changes to Amanda's TRUST and ADMIRATION for the PC and Joe.
In that scenario the game has responded appropriately to the event with only a generic understanding of its type (RUDENESS). By referring to the events vaguely and euphemistically, referring largely to location, time and participants, the game makes use of the player's recall instead.