Answer by Scott Ford for single keypair for all regions

You can also do this do the region list with expansion to get the list of regions dynamically...

for region in $(aws ec2 describe-regions --all-regions --query "Regions[].{Name:RegionName}" --output text | tr '\n'''); do
aws ec2 import-key-pair --key-name MYKEYNAME --public-key-material file://~/.ssh/MY_PUB_KEY.pub --region $region; done