I've known NFs who were not boring. Treakly is more my reaction, if I have a negative one. Like WWF and harlequin romance covers and taking JRPG stories very seriously and thinking of the children and responding to a logical argument by saying "But isn't X what really matters?" in that lifetime movie of the week voice.
Oprah-itis. That's the ticket.
Not all are like this by far, but it's a tendancy I've noted. I don't know if I'd call it boring. Mundane, maybe?
Anyway, all types have their own mundane shit. The NT's fascination with obscure systems can often be boring to everyone else in the world ("I'm cataloguing MOSS!!"), SJ's need for routine and order leading to everyone having fun in an orderly, scheduled fashion, and the stereotypical SP hedonist who killed just a few too many braincells.