I disagree. That's honesty. It's no real excuse to say "Because I'm lazy" as it will do nothing but make you look bad and unreliable. A real excuse is something like "I had to finish this other thing first" even if you actually had no other thing to do or it took all three minutes to finish it, and you lazed the rest of the time. Nevertheless, the aim is to make it appear as if you were too busy to handle what you were told to do, and so it wasn't your fault it didn't happen. But being lazy is always your fault.

Besides, it has always kind of bothered me when somebody asks you to do something that isn't urgent at all and it doesn't matter when it happens, yet still expects you to drop your own stuff to do it immediately, instead. And then when they come back and it's not yet done, as you planned to do it later when it's more convenient for you, they don't understand and consider you lazy.