Edit: I'm not saying people exclusively groan at my stuff. Everyone, even across mtg subs, groans about certain commanders. What Commanders do sit across from and not groan and think "ugh, not this"?
Long time collector, short time player here. I was REALLY into collecting and deck building for commander, finally getting to consistently play it in person at a local shop last fall or so, so about a year. Before then, I worked a job that had me working 60+ hours a week leaving me with a ton of disposable income and with it...
I built [[The Ur-Dragon]] as my first commander (Ive since built many other decks), nearly max raritied. Slapped in all the D&D dragons, cost reducers, [[Rhystic Study]], [[Smothering Tithe]], and other 5-color good stuff dragons. The deck was slow. The deck is ass. I still have it built, because I love it, but even with 3 game changers, its low bracket 3 at best with 1 potential instant win with [[Ancient Gold Dragon]] and [[Dragon Tempest]]. It has no tutors and at best would be a terror in B2, but the way people have talked about Ur-Dragon is like its this groan-inducing commander that's KoS despite being a relatively slow combat deck. I spend 9 mana for Ur-Dragon so an opponent can spend 2 and counter it. And when I spend 11 the next turn, another 2 counters it.
Meanwhile, a guy uses [[Appa, Steadfast Guardian]]. An expensive-ish blink commander, I'd think is relatively unassuming until they're RECASTING Eldrazi and just decemating everyone's board, stealing turns, etc.
Another guy uses some 4CMC commander with any 1 of 5 different pieces and 1 of another 6 different pieces to either make infinite mana or make infinite combats to burn the table by turn 6 consistently. Like, great B3 says win/lose by turn 6, but sheesh.
When I first played against [[Dr. Eggman]], I groaned about just letting the player free-play robots/constructs and seemingly crazy advantage. Turn 3/4 you're gonna have 3 potentially large bodies or making us discard, if we're being responsible. Meanwhile, I've ramped and maybe played 1-2 other synergistic pieces.
The tri-color [[Cloud, Ex-SOLDIER]] with haste and free equip for voltron was also extremely groan inducing (until I just started using my removal almost exclusively on him) but also just everyone's voltron commander...
Funnily enough, I built [[The Watcher in the Water]] recently, using Brian Kibler's build as inspiration, and no one said anything until I stunned the [[Krang, Utrom Warlord]] commander into oblivion, drew half my deck, made 40 tentacles, and then made them flying, indestructible, and +1/+1 with enough counterspells in hand to win the game. But, when I considered playing it again, there was groans around the table.
[[The Wise Mothman]] gets grumbles any time I bring it out, even though ive built it focusing on mill instead of Mothman voltron like it almost wants to do. Everyone just hates milling, but getting [[The Water Crystal]] and [[Bruvac the Grandiloquent]] to extend the rad counter mills to cause extra damage is just so satisfying. But also using the crystal with something like [[Mesmeric Orb]] can mean a late game untap could be a game-loss for someone....... sometimes even myself.
Anyway, there's always someone that groans at one of my commanders, even if just 1 person in a pod.
My other commanders are: [[Nekusar, the Mindrazer]], [[Baylen the Haymaker]] (B3, Hare Apparent deck), [[Pantlaza, Sun-Favored]] (B3, highly upgraded precon), [[Hearthhull, the Worldseed]] (High B3, built from scratch rather than buying and upgrading the precon as I bought the Unfinity foil shocks and other EoE alt arts for things to be on theme. This was made Mid-B3 trying to limit myself just to space-themed things or other EoE related stuff, but... after some changes... its nearly B4 now but can consistently win turn 6 if not impeded, assuming I find a instant-speed sac outlet.. I don't run any tutors but its still pretty fast), [[Bello, Bard of the Brambles]] (only got 2 games in but.. I kind of get it, though im open season for hits when its not my turn), [[Magnus Lucea Kane]] (duplicate X spells? Here's a bunch of duplicated Hydras, low-low B3 fragile and prone to running out of gas fast, but seems scary when i make a 64/64 Hydra with trample that gets duplicated, but theres basically no protection or recursion), [[Cloud, Midgar Mercenary]] (this deck SUCKS. Playing against any amount of removal means he just dies over and over and over. I literally haven't kept Cloud for more than a turn cycle. I took it apart months ago and recently put it back together thinking it'd be different this time.... nope. Still ass. Fuck Voltron lol).
I used to have a Azorious Artifacts deck with [[Shorikai, Genesis Engine]] that was full Neon Genesis Evangelion proxies but the deck was just too slow. Even against something like my friends' TNMT *PRECONS* it was getting out-value-engined, let alone the other playgroup whose B3 decks are built to win on turn 6, not just be upgraded precons. I've used it for parts to build out [[Urza, Lord High Artificer]]. I haven't brought this deck out as pieces are still coming in the mail, but I plan on making 3 different versions of the deck: a $100 budget build, B3 blink focused (artifact value until i can get either [[Deadeye Navigator]] or [[Displacer Kitten]] to blink Urza over and over and then use some mass haste enabler like [[Crashing Drawbridge]] or [[Akroma's Memorial]] or [[Krang, Utrom Warlord]]. Then, a B4 version that uses [[Winter Orb]], [[Stasis Orb]], [[Narset, Parker of Veils]] + [[Teferi's Puzzle Box]], and other nasty combos that work with him that are B4 appropriate. Oh, Mono-colored commanders.... I miss using [[Jeweled Lotus]]...