Discussing former UK Prime Minister Margaret Thatcher, 48-year-old Coyle took offense when Downton fan Roberta Knighton told him she thought the comments he was making about the former PM were "beneath him."
The BAFTA and Emmy-nominated actor was quick to hit back, "Hard to know how to respond to that … but go f--- yourself feels about right".
"You have no idea what is beneath me … PS go f--- yourself x."
Coyle plays much-loved character Mr Bates on the British period drama, which is heading into its fourth season (the third will air soon on the Seven Network).
View slideshow: Downton Abbey