柠檬不酸芥末不辣
[níng méng bù suān jiè mò bù là]
Lemon and mustard each have characteristic tastes, so calling oneself 'lemon not sour and mustard not spicy' suggests a personality where the characteristics should exist do not, possibly implying they don't show strong emotions and remain unimpressed by anything, having seen it all or been dulled to usual stimuli. But it also carries lightness, making the statement sound playful rather than totally negative.