The unpredictability factor.

[Vexatious]

I think you can tell pretty quickly if an opponent is an idiot or just using gimmicks. After a glimpse at one of their gimmick pokemon, you know what to expect from then on. For instance say they have a pokemon that uses an obscure but useful move. Like Aerial Ace on Scizor. Standard Choice Band sets like Bullet Punch, Pursuit, U-turn, Superpower. However if they use Aerial Ace they obviously hate machamp and would rather kill it then u-turn away. From that point on realize that they may have edited their pokemon to handle threats they normally don't handle as well.
However in the other case, you can also tell if they just don't know what they are doing. I was playing a friend at college on battle revolution in front of our whole group of friends (he claimed to be a pokemon master and what not so I challenged him). I led with forretress to start setting up asap and he leads with Gyarados. I think to myself "Hell yeah awesome" Then he uses Fire Blast in my face...I just stood there confused and laughed. Then I sent out Azelf and 5-0'd him with nasty plot.

My point is there tends to be a visible difference between gimmick and stupid. Once you've decided what the move was, you can better predict the rest of his team

 

[MK Ultra]

I find a lot of players less well-versed in pokémon tend to not use things that for smogonites are near-constant; they're highly unlikely to use spikes/t-spikes/sr, less so a spinner, and never (on purpose) a spinblocker. They also tend to not understand tiers, but more the concept of a legendary - Mence and Chomp are perfectly fine, but Articuno? Not a chance. Most people don't realise Hidden Power's er, hidden power, and therefore you can safely switch, for example, a Swampert into a Magnezone. While unpredictable things can throw you off, there is no way anyone should lose to someone who thinks Sableye is useable. (Yes, someone has tried to explain it to me.)

 

[Thats_PM]

I say, if you can't beat them, make them join you!(if you don't stand them for being too random, show them the ropes!) I met a lot of people who weren,t aware of the metagame, tiers, and how to train a pokemon decently. (and still have some whom wanna fight me :P ). What I would do is, switch in less, and don,t use dedicated walls. i.e. don,t switch Blissey into Jolteon, it might double Kick you :O (lame example I know, as a random Jolteon will do like 20-30%dmg with it...). Instead, run stat uppers or high speed all around sweeper(LO will be prefered too). Outrage/ Draco Meteor also gets a special mention. They might know steel is it's only resistance, but they probably will try to revenge kill you instead of outright walling you. Stall should work fine too ( not walling, but more stalling) i.e. subseed(jumpluff!) parafusion lanturn, scarf jirachi/air slash jirachi, tormenTran. Dual screen will be usefull too, as if they are "noob" they will most likely rely solely on power to beat you.

 

[WhimsicalBox]

Another aspect of non-smogon battling I've noticed is an aversion to switching, despite the lack of entry hazards. It's weird to think you would keep in a Rhyperior on a Venusaur. It's almost always an instant KO, and it's stupid to throw away pokemon that have use. One of the more fun aspects of battling non-competitively is you can use different movesets and succeed anyways. I had an amnesia slowbro that was unstoppable with my heal-bell miltank. Stat up, slack off and sit on your ass while you slowly chip at their health...

 

[Flashfires]

I've noticed this effect in a lot of games when playing with less competitive players. You make, what are to you, the obvious choices and you suddenly find yourself flat-footed as your opponent decides to do something no decent competitor would ever do.

 

[Treadshot A1]

I faced a guy yesterday and 6-0 sweeped him. I think you know they're not competitive when they ask for Open Limit battles. :)

 

[athurart09]

You don't. Unpredictable = Gimmick until it becomes very good.. in which case it becomes popular. Then it loses its predictability. On the ladder you will lose to some knucklehead with a gimmick, then you fight him again you won't make the same mistake. Its the cycle of pokemon.

I also think so.