A long time ago the (year 89 or 90) the reason behind Dilbert's tie... !$%*!$%*! was approached. Dogbert proposed that Dilbert's tie can't stand to be near him.
In another strip Dilbert's tie is straight after he might've gone all the way with his girlfriend.
Some postulate that Dilbert's tie is up as a sign of his total lack of style and fashion from being and engineer. That is, if he has an apparel anomaly he wouldn't notice or care because style has no practical application or function.
I've always thought the latter.