Some of the best, kindest, most successful, and un'trashy' people I know have neck/hand tattoos. Some of the worst, most spiteful, drug dealin, and scummy people I know drive really nice cars and wear suits.
Stereotypes aren't always true... but they exist for a reason, because more often then not they are true. Being or knowing an outlier doesn't make that any less of a fact. Most people with neck tattoos are shitty lowlifes, so its natural for people to think shitty of them.
Though I, personally, believe in the old adage 'don't judge a book by its cover'