Anything small, over weight, underpowered, tapered wing with no washout and with the CG at the rearward limit.

These are often scale or semi scale models that fill the eye in the shop and are a challenge to keep airborne. There were a number of kits and plans for 25 sixe models in the UK that met these criteria and the test pilots in our club would go and hide when someone arrived with one of these. Nowadays they are getting rarer but still turn up at swap meets. I know I bought a Spiteful with retracts [ because it was cheap ] and boy was it a handfull even with a good engine on song. It would flick roll on take off and everytime I pulled any real G. I lost it when it spun in.