If you have nothing nice to say then don't say anything at all.
I know we've all heard this as a child growing up but it is so true. Not just because you may or may not hurt my feelings but more so - I don't want you to rain on my parade. I like to think of myself as an upbeat, happy go lucky person who tries to find the silver lining in any situation. So when you come waltzing into my life with your crappy attitude I want no part of it. I don't have the will power to keep from stooping to your level. So do me a favor leave it at home or don't come around - it is as easy as that.