Ne isn't impulsive, in the realm of the world, unless the payoff is somehow feeding Ne (which is, it feeds the intuition). This means that, in an ENTP, we are impulsive only when it comes to latching onto new cerebral ideas and the desire to implement them (but not actually doing anything at all). For the ENFP, it's an impulsivity towards activities and people that enhance their sense of self or how it relates to the human condition, and make them feel most in tune with their notion of who they are (but again, rarely making adjustments to actually implement any changes). So, in a sense, ENxP are the least impulsive of the types - and in fact are often plagued by inability to take action at all, preferring just to dream and imagine it instead while letting others push to action. A "crazy" Ne dominant just has no lasso on what is believed to be possible, and is not properly utilizing Ti or Fi to filter. To the outside world, this comes off as eccentricity, but definitely not impulsivity.
Se dominants definitely come across as "crazy", when Ti/Fi aren't properly preventing Se from seeking a push into action. Se is the provakateur, the function of action - the desire to seek out and do. NJ types can also manifest as "crazy" in the realm of impulsivity, when under great stress - activating the Se function as the preference. In NJ types, since they are typically much more calculated and subdued, the impulsive action might seem quite out of place to the observer. In SP types, it will seem like they are just born that way (without reflective thought, driven to action).
