Stop feightin' ! Cold water soak straight away. Gentle squeeze 'till it fades. Allow to dry naturally.
And here's me thinking Here's a guy in real bother - I'll not suggest Vanish 'cos he'll have to go to the Spar an' it'll take ages and they'll look at him and say huh, what's that?" and by the time that happens it'll be fixed in so i'll give him the old fashioned quick solution. and then realised you were pullin my pisser.
For future reference. Blue blood gets out red blood every time. So if buckingham palace is closer then the Spar, your cold tap and the cupboard under the sink. Inflict a small wound (or large depending on the amount of blood) on a member of the royal family, preferably Charles, and apply the blue blood to the soiled garment. Hey presto! in a Viz type manner..