I just rented a Tarmac w/ a 105 groupset, 52/36 and 11-25, for 2 weeks in Italy.
I know cross chaining should be avoided at all cost, but from my exprience when doing so under distraction it simply causes noise and accelerated wear.
In this case, when cross chaining on the 2 largest cogs (52 in front, 25 in rear), the lower pully is extended beyong its boundaries, to the point where everything blocks. The pedals will no longer turn even under high wattage. I have to get off the bike and take the chain off manually by hand.
The italian guy at the rental place litterally shouts after me and gets really upset when I tell him this is not normal and there is either a problem with the chain being too short, or something else. He yells that I should never ever cross chain, as if I was trying to kill somebody... I know we should not, but sometimes it does happen.