I have never vaped anything but I am guessing that some people are getting nicotine poisoning from overdoing their nicotine vaping. And they can abuse and increase their nicotine intake precisely because vaping is much less irritating and less harsh on the lungs than cigarette smoke.
The only modern known deaths by nicotine poisoning have involved pesticides containing nicotine. There have been a couple recorded incidents of nicotine intoxication by people who have drank the straight solution (5-10ml of 24mg or greater nicotine solution.) NIH estimates that the required ingestion would have to be in excess of 3000mg to reach poisonous levels - for say the solution in JUUL pods, that would mean drinking the straight solution from more than 120 pods.
I buy 100ml bottles of a high nicotine solution per prescription for migraines, I'd have to drink 1.2 bottles of it to reach toxic levels and I guarantee I'd be vomiting with just a tiny portion of that amount. Those bottles last me about 4 weeks.