16. Staredown With The Undertaker At UFC 121
Throughout the course of their history - or at least since it became apparent that the two were competing for at least some of the same fans - the WWE has generally frowned on crossovers with the UFC, even outside of the octagon. So it certainly caused a stir when The Undertaker showed up to challenge Brock Lesnar to a bout at UFC 121. The confrontation happened in the stands, and the controversy stemmed from the fact that, at the time, Lesnar was still under exclusive contract to the UFC - which is why the match between the two wouldn't happen for years. Sure, it was a work, but it was still a pretty controversial one, all things considered. While The Undertaker was the instigator in the stands, don't think for a second Lesnar wasn't a willing participant.