The 26-year-old, who has been dating his Pride + Prejudice co-star Knightley for more than two years, is a regular target for press photographers because of the high-profile romance - but the unwanted attention has left Friend fuming.
And he insists he wouldn't hesitate to hit out at a snapper if they overstepped the line.
He says, "There's 15 big hairy guys one foot in front of you, walking backwards with 15 flashes going off. It's right in your face, all the way to the shop, all the way through the process, and all the way back.
"I now understand entirely why people take swings at photographers, and if one gets within more than a foot of me I will do the same.
"I have absolute respect for anyone who manages to knock one of them out!"