Every time they tried to talk on global I'd respond by just going "shhhhhhh quiet time" over global.
Don't be a dick on the internet, problem solved.
No. What he was doing was an incredibly tame version of what anyone will do on the vast majority of Arma servers. You just don't talk in global. Keep it in group/direct/vehicle/ maaaybe side but most likely not. If you think that is being a dick, you must be new to the internet.
Spamming chat repeatedly after someone says something isn't being a dick? He got what he deserves. Maybe next time he will think twice before spamming.
Just because the internet is full of assholes doesn't make one person being a dick any less annoying.