I would caution against standing on the pegs if there is a very good chance you will either need to brake hard or swerve. Both of these are much harder to do if you are standing and I would go as far to say no-one could do either as well as they could when sitting.
There was a very long thread over on advrider where folks recommend standing on the pegs if someone is tailgating you. Consensus was it really works, I guess it does get folks attention or at least make them worried you might fall off and damage their car! But personally I wouldn’t do it in front of a left turner.