Gate agent in YYC the other day (domestic) made a pre-boarding announcement about 5 minutes before boarding began, that amounted to YBYL.

I don't recall the exact wording but it was something to the effect of "We will be processing the upgrade list about seven minutes after boarding begins. If you are waiting for an upgrade, do not board the plane. If you do, your upgrade will be cancelled."

I know others have mentioned hearing this one on occasion before, but it's the first time I've heard it myself. (Then again I'm usually trying to time my arrival in the Zone 1 line with the boarding time so I miss these things a lot)