It doesn't get much "cheekier" than this. Microsoft had the audacity to put a "Switch to Windows Phone" App on the Google Play Store. So far, Google has stuck to their "open" (mostly) policy and left the app there despite it being negative advertising against their own branding. Of course, even if Google is just doing the right thing by adhering to their own open policy, it also turns out to be pretty crafty to leave it there. For the most part, Android users have slammed the app by giving it the lowest rating possible.
It seems that whenever Microsoft tries to get clever with their marketing strategy it just completely backfires on them. You would think they would figure out that blasting your competition with negative ads almost never works.
Source: Google Play Store - Microsoft's Switch to Windows Phone App