I have seen the self upgrade done successfully twice on the BLR-CDG (AF) route. The second cabin of the A330 is almost always completely empty so I always take a seat there (as a regular C pax). More often than not an pax from whY moves up there, settles in full sleep mode in 10 seconds and pretends to be fast asleep. The FA's always try to awake them or argue with them but they (always Indian pax) just become very agressive and the (often all female) cabin crew just leave them there.
Last time when I asked "why? how? but?" they just shrugged and said "it happens so often we get tired of fighting it".
Never ever was there police waiting for them at CDG. Pretty piss poor handling I think.