Scent combo no-no's...

I'm curious to hear what experiences folks have had with products with scents that, standing alone are great, but when combined, unexpectedly generate undesirable scents. Obviously, with some potential combos, it doesn't take a rocket scientist to figure out beforehand that the combo probably won't work. But sometimes we think, hey x shaving cream should nicely complement y aftershave or z cologne, but then you find out that the combo doesn't work...

I'm not limiting to any one or two shaving-related products. Whatever combos you think don't fly -- creams, soaps, pre-shave products, after-shave products, colognes, deoderant.... you name it: if you tried but failed, please share.