Ds1 is 16mo and he literally laughs into face on the relatively rare occasions I use a 'cross voice' with him!! (when he won't lie still for his nappy change after much cajoling and gentle bribery, when he puts his hands in his own poo for example).
I don't do it often but I was hoping he would at least be shocked into stopping what he was doing...but nope! Doesn't care!