What you'll need:
Fabric of your choice (cotton or jersey will work best)
Set square or anything with a large right angle
Sewing machine / needle and thread
*note* If your bib was like mine, it had a flannel front with a plastic back. I left the plastic backing in place but you can always remove it.
Take one boring white bib. Using your set square, draw a triangle ON THE BACK of the bib. Cut along your lines.
Trace the shape of the newly cut bib on the the REVERSE side of your fabric. Cut.
With WRONG sides together, sew all around using your sewing machine. Make sure you leave a space for the velcro fastening (not sew over it like I did and have to unpick).
Tidy up your edges with your scissors and you're done.