Being OP (over-powering) in flight sims is mine.
Example; in IL-2, I set myself as P-47 vs 16 ww1 aircraft. Head-on passes. Over the top attacks. Much fun.
In DCS. Take a F-16 with guns only vs boxed formations of B-17. Goal is not to get hit.
What’s yours?
Anti aircraft systems & artillery. DCS is pretty good for this.
Did a challenge with friends way back having dozens of artillery guns fire on a rectangular box down a road - the “gauntlet”. Challenge: drive a Humvee through and live.
Playing as AAA guns and SAMs with CA in multiplayer can cause quite a surprise to an unfortunate person.
Both @AndyE and @Franze have learned that flying near tanks and SPG’s when I am in CA is not safe, you may find your radar dish perforated with a sabot or your KA-50 taking a shell. 
With the Hornet I practice standing it on it’s tail for fun. Hovering just varying afterburner stages.
Manual bombing. Lately anyway. Old School. Very satisfying.
Airshows. I enjoy planning and flying the perfect routine. I spend a long time in the planning and practising stage and then I fly it and watch it back with great satisfaction and an extremely critical and self deprecation bordering on impossible to please. I love it.
Oh and tailslides and cobra as well. The perfect cobra eludes me. I’ve done some absolutely stunning one (if I do say so myself) but I’ve never ever let myself believe I can’t do a bit better. I did a tailslide in the flanker on DCS that my recovery altitude was in in single digits. Glorious game to play
My personal ground-attack training mission, in various planes. Setting up lots and lots of targets and making as many big booms as possible.
Awesome thread topic is awesome.
Yes, I’m with you on what I like to call “deer hunting”; ie setting up situation against enemies that can’t really fight back. It’s also good for training. E.g. in IL-2 1946 I’d intercept flight of obsolete bombers to practice general airborn gunnery. Same with DCS and hunting large transports. Good for figuring out how radar intercepts and missiles work.
Oddly, it’s sometimes fun the other way around; Some of the most fun I’ve had with BoX is flying ‘Tante Ju’ to and fro the front lines while dodging marauding fighters.
Recently extended this to Cold Waters; gave myself a 45 knot capable Seawolf that was as quiet at 20 knots as a LA class at 5. In line with the way she’s described in the novel I’m reading (attack of the seawolf) and cut a bloody swath through the south china sea.
I need to do this more in CLOD.
Busting up poor hapless AI bots in DCS. Listening to MBMBAM while flying to and from the front in Il-2.
But my guiltiest pleasure is partaking of the herb and then doing long cross-country flights in something without FBW. I rarely do that, but boy is it a good time! Flying’ high 
That made me belly laugh. God I love the Netherlands
Flying a huey around Nevada with YouTube playing one of my play lists 
Flying DEAD in the A-10C. Extremely challenging but a lot of fun. Basically loading the A-10C up with Mk82Air, staying below 100ft for the most time just popping up shortly to engage the SAM site and then dipping down again to run home
Landing below minimums in IMC without ILS in the DCS Hornet - especially with rocky clouds near the runway .
That aint no guilty pleasure, that’s just being a cool badass virtual fighter puke. Well it is if the SAMs you’re beating up on are above the SA-5 variety
Sparring with an SA-2 site is fun in a relaxing way, like sparring with an overweight beginner in martial arts. He’s slow, he’s easily countered but if you sit still it’s gonna hurt.
Actually, come to think of it, in a hog a Guideline might be fairly dangerous because you’re so slow. In a viper they’re easy to run dry.
Honestly…the entirety of flight sims is a guilty pleasure. I don’t have to make radio calls, I don’t have to fill out paperwork, I don’t have to fear a NOTAM is going to ruin my whole night, etc…etc… It is just a nice change from the daily professional routine.
And I bet you’d get in serious trouble landing your maddog with a margerita in one hand and some dutch pleasure in the other
Yeah…there is that too…! That is a major one!
Usually Skynet controlled IADS with overlapping SA-6, SA-11 and SA-10 sites which are protected by SHORADS of all kind. I have about a 55-67% succes rate with tat xD
Seems like I should have some but I don’t really feel guilty about any of them. Maybe PvP gunzo dogfights because it seems to be something that a lot of players in modern jets have great difficulty with in execution. Too much reliance on high-tech missiles seems to dull a lot of player’s abilities to handle the basics with using the gun and maneuvering close in. But usually when I do that, I’m trying to teach others how to do it as well, so I can’t really say I feel guilty about it.
I fly the Huey with the CCR (guess which song) with a mix of generated weather (usually pretty bad) and randomized vehicles with HMG.
Trying to go from one airport to another flying low.
I crash a lot. But it’s cool.
You just quoted my personal flight sim mantra!