Probably the gender thing, so I wouldn't be accidentally cannibalising babies.
That said, it might be very painful to rapidly change gender (providing we're meaning my entire body changes to a female one), what with my hips changing shape and my breasts expanding, let alone the mechanics down below.
Also, I get hayfever, so I could have a blast of 5 sneezes in a row, which would be alarming.
I suppose I could theoretically control it though if I had some sneezing powder, to either change at will or change back after an accidental change.
So, yeah, sneezing love change please.
Would you rather sweat blood (without it leaving you suffering from blood loss) or have two living heads?