A: You have to revisit them occasionally and get re-angered by them. That futile rage can then be transferred to a grumpy workout, an angry clean of the house where you stub your toe every two seconds or a long, drawn out bitch session. The options really are endless!
B:You have to keep accurate notes that includes names, dates and places . Email is an especially good place to start a grudge because then you've got long lasting proof of what caused the initial riff. Without accurate notes or a memory like an elephant, the facts get confused and grudges can shoot off in completely fictional directions. Be a drama queen by all means, but be accurate.
C: Get your common social circle on your side. Put a bug in nanna's ear, teach your three year old niece how to say "aunt rosie is a bitch" and make sure every single one of your friends hears your side first. Strength in numbers.