The *ception thing is just a reference to how, in order to achieve the film's titular effect, Leo + crew had to create a good many levels of dreams within dreams. It's just a meme. Get over yourselves.
Anyway, the evergreen "biggest possible explosion" was ours, in the original GTA. Keep stealing cars, out of sight of the cops, and abandon them all in the middle of the road. Also punt NPC cars into the snarl, so everything's closer together. Extra points for trapping cops etc, super points for fire engines. Get a few trucks and school buses in there.
Then once the pile is big enough that the game starts to have trouble keeping track of the cars on the outer edge, grab your rocket launcher (or heck, the pistol), retreat to a safe distance, and... yknow. Making sure to follow the track of the explosion so you get all the points and multipliers for it.
Turning on debug mode and seeing if you could get the petrol tanker up to 136mph (the highest I ever saw was 141, in one of the sports cars) for the second time ever was always a good way of killing an afternoon. That and blowing up ALL of the fire engines. GTA had a limitless supply of cop cars, but only a finite number of fire engines. Once you had helped them all to achieve their nominative destiny - i.e, becoming fires - no more would come when you blew something up. Can't remember if this caused a problem on that one mission where you actually had to steal one, though...
Low-gravity long distance rocket jumping in Quake...
Snail races in Gran Turismo, even better in GT4... get two identical (except in colour) examples of the worst available car, and have the winner truly decided by who's the better driver, rather than who has the most powerful engine. Advanced mode allows you to modify all parts of it ... EXCEPT for doing weight reduction, adding nitros or tuning the engine. Strangely, this would often come down to who was best at balancing the gearbox ratios, especially on hilly courses. (Nightmare mode: Nurburgring. The most recent car used for such a race was a tiny japanese van from the 60s. I figured I'd try to beat Sabine Schmitz in the Transit. I had to tune the thing (including engine and weight) to the absolute limit and do a once-in-a-lifetime godlike drive (the B-spec autopilot hadn't a hope) to manage a 9:57 in it... Now consider that the tune-up removed about 25% of the weight and increased power by more than 150%... and that the gearbox alteration raised Vmax at the limiter by about 50%... you've got to be seriously bored / committed to do that track with an unmodified one. However, Costa Di Amalfi tends to be the hardest, as - like the Tahiti Rally in GT2 - it has a couple hills that some of the lowest powered, skinniest-tyred cars literally can't get up without a radical gearing tweak and some soft-compound racing rubber...)
...note that this one tends to leave you prey to being completely annihilated by the cheating bastard AI, who will turn up in cars eminently much faster than yours even when you've souped yours up and they haven't, unless you turn down the difficulty. That then means you get less A-spec points, if any at all. The "average" of 100 is damn near impossible when snail-racing, because the 10hp or more difference it obviously thinks is perfectly acceptable for a top fuel Le Mans single seat racer can mean the pack disappears away from you over the horizon by the first bend and you'll never get the drop on them... unless it's an exceptionally technical track, you've tweaked the car to perfection, and you drive as if you're the stig's elephantitis-benighted cousin, taking advantage of the AI stupidity.
NB GT4 takes the piss a little with the inclusion of the Benz Autowagen and other pioneering vehicles, which are so chronically slow and underpowered that - combined with an inability to make any changes to the hardware as it's a "special car", and the infamously stupid rev limiter behaviour - it takes any sense of fun or competition from the game. You end up having to set limits, e.g. nothing below 15hp...
Going for the biggest possible jump / most extreme possible flip / fastest reverse gear speed, or fastest possible laps in the Prius using ONLY the electric motor (meaning you have to press the accelerator very gently, and balance maintaining speed whilst coasting vs regenerating battery charge by braking slightly)...
For a driving game triple threat, mucking about with the Driver config files to make the special turbo car playable in "take a ride" mode and going for the biggest possible jumps, with bonuses for breaking the game engine as a result. Even better, either turn on invincible mode or extra-super-speed (which meant you could cause far more damage than you took with each hit) and create total carnage of the police cars. Points for the furthest distance you were able to punt one across the map.
(For Driv3r, this became simply "can you drive from one end of the map to the other in a normal car without being killed?". I mean, I knew Miami was a bit dangerous, but... Nice? Is it really that deadly a place to live?)
Playing Final Fantasy characters along "career" paths that are completely against their supposed "type"...
(been doing this on and off with FFX, apparently I'm in for a complete ass whupping when I get to the final boss. We'll see.)
Recreating your hometown in Sim City then attacking it with disasters. Though this might actually be the point, IDK.
Making a party of naked adventurers in Dungeon Master and seeing how far you get (...ditto).
Creating the most masculine possible woman or feminine possible man (using default models) in Second Life and seeing if anyone notices.
... blah blah anything else that pushes the game engine near but not across breaking point in terms of what you're allowed to do
