Comic sans was never trendy, as such. Instead, its ubiquity was due to the fact that:
a) It was included in the default font set of just about every computer sold from nineteen-ninety-something to today, and
b) It was the only default font that was "fun" and "not boring" to the great unwashed masses of typographically unsophisticated people (a category in which I include even myself)
So everybody from teenagers to grandmothers would look through their font list and go "boring, boring, boring, ooh this one looks like handwriting, that's fun, I'll go with that". The other reason it's derided is therefore that it's used by design-naive people and hence associated with bad design; Comic Sans is very likely to be accompanied by flashing pink text and ugly clip art.
While writing this, I suddenly noticed that the expenses reimbursement form sitting on the desk in front of me is in Comic Sans. So add "HR reps" to the list.
a) It was included in the default font set of just about every computer sold from nineteen-ninety-something to today, and
b) It was the only default font that was "fun" and "not boring" to the great unwashed masses of typographically unsophisticated people (a category in which I include even myself)
So everybody from teenagers to grandmothers would look through their font list and go "boring, boring, boring, ooh this one looks like handwriting, that's fun, I'll go with that". The other reason it's derided is therefore that it's used by design-naive people and hence associated with bad design; Comic Sans is very likely to be accompanied by flashing pink text and ugly clip art.
While writing this, I suddenly noticed that the expenses reimbursement form sitting on the desk in front of me is in Comic Sans. So add "HR reps" to the list.