TTCSI Case #4 - Clash of the titans

Case #4
The accused: Tek Saavy (I would hyperlink for them, but I don't want to generate any traffic for them)
The crime: *cringe* Using Arial and Helvetica...together.

When you pass these posters plastered around the TTC, you might not think much. They are pretty no-frills, with white text on black background. Overall, kind of sombre, unoriginal, and not very attention-grabbing. But wait... it gets worse.
If we look closer, the designer has committed one of the worst typographic crimes possible.
Either through carelessness or ignorance, they have use Arial for the majority of the text, and Helvetica for the website. This is made obvious by the terminals on the upper case "C"s and "S"s. (For a slightly better comparison on Arial vs. Helvetica, click here)
Ruling: Arial and Helvetica are like two unruly children that don't play well together. I have my own preference between these fonts (read: I really dislike Arial), but I am willing to let Arial pass under certain circumstances (ie. availability to the designer, irony, etc.). But please, for the love of typography, do not use Arial and Helvetica together. Ever. Please.