The Jujutsu Kaisen fandom has a running joke about Megumi Fushiguro summoning Mahoraga at the slightest inconvenience. Sometimes it seems like every time he spills coffee or has a weird birthmark on his finger, he calls the King of Curses to deal with it (and there are tons of memes online about this). But it's kind of silly to look at this through that lens, because Megumi doesn't just willy-nilly use Mahoraga any time he's in a difficult situation.
If you look at all the times he either thought about summoning Mahoraga or actually did summon Mahoraga, each of those was based on a real threat to his life. The funny part about this whole meme-ified phenomenon is how fans have taken humor out of the context of these events; when we look at the events leading up to these moments in Jujutsu Kaisen, the motives for calling upon Mahoraga make perfect sense.
The First Attempt: Fighting Sukuna Made Perfect Sense

The first time Megumi wanted to bring forth Mahoraga in Jujutsu Kaisen was when he faced off against Sukuna, who had possession of Yuji's body. This wasn't some petty fight; it was literally the King of Curses in total control.
In this moment, there weren't any other choices Megumi could make to save himself. He was going to die for sure at the hands of a guy who could beat him in all areas. Mahoraga was a last-ditch move that Megumi pulled off.
Some people laugh at Megumi's choice; however, those same people ignore the fact that going against Sukuna is an extinction-level event, not just a "slight inconvenience."
The Second Summoning: Exhaustion and Overwhelming Odds

Megumi's second attempt during the Shibuya Incident was significantly different than his first attempt due to his context. He had previously been ambushed, leaked cursed energy, and was exhausted after battling against a special-grade curse. After this ordeal, he then faced his father, Toji, who was possessed by a cursed spirit.
This compounded the problem for Megumi in Jujutsu Kaisen, as he was now confronted by two catastrophic threats in a very short time frame. While he was ready to fight when he activated his Domain against Dagon, he wasn't in any shape to be in front of someone with Toji's skills when he was feeling this way. His only real option at that point was summoning Mahoraga as a desperate last-ditch effort.
The Third Instance: Sister Possessed, Body Stolen
Megumi's third summoning attempt came after his sister, Tsumiki, was possessed by Yorozu, who then proceeded to steal his body for Sukuna. So, basically, Megumi lost his sister to someone else's body, and a lot of chaos has been happening at once. This represents arguably his most justified use of the technique.
With the stakes so high, it wasn't just Megumi's personal feelings that drove him to use his technique when he summoned Mahoraga. It was literally his life. When all you see in front of you is impending doom, it can give you a greater sense of urgency.
The Todo Exception: An Actual Minor Situation

There’s one time I agree with the criticism, and that came in the very first season when Megumi nearly summoned Mahoraga to fight Todo after a relatively minor altercation at the Sister School Event. While it was an intense fight in Jujutsu Kaisen, it was not nearly as close to being an existential threat as all his other summoning attempts.
Even though Todo is really strong, he wasn't trying to kill Megumi. He was trying to be more like a bully to him. In this specific case, summoning Mahoraga seems a bit over the top or uncalled for, given the way that Megumi got bullied there. However, one questionable decision out of multiple attempts doesn't justify the meme that he summons the shikigami for everything.
Every Fight Was a Final Boss Level in Jujutsu Kaisen
In Jujutsu Kaisen, when looking at Megumi's fight history, one thing is obvious - there is a clear method to the madness. Megumi fights against things that will kill not just one sorcerer but multiple, not a common threat or a "normal" cursed spirit.
The only fights he has had since he was introduced to us are against special grade cursed spirits, legendary fighters, and the likes of Sukuna, Toji, other special grade cursed spirits, and long-dead sorcerers. The statement about using Mahoraga as the summoning spirit for "anything" becomes untrustworthy when you take into account that at least 80% of Megumi's fight history are literally final boss level encounters that most of the rest of the cast wouldn't even survive.
While the Jujutsu Kaisen fandom's jokes about Megumi summoning Mahoraga in school zones and over coffee stains are genuinely funny, they don't reflect what happens in the manga or anime. Most of his summoning attempts occur during life-or-death situations against opponents who vastly outclass him.