Sorry, hit send too soon.
Night Fishing - usually involves a vast amount of expenditure and time.
If he's into large carp, it is best to run away now, lest you get dragged into conversations about what brand of boilie is best, find out he's just spent three hundred on a radio controlled bait boat, he's used his annual leave to go and fish in a lake somewhere in France or sodding Ebro for the catfish and find yourself constantly surrounded by dark green equipment involving full camouflage clothing, bivvies, umbrellas, chairs more expensive than a three piece suite, rods, unhooking mats and everything smelling vaguely of rotten Mackerel (as per the boilies and various extra oils you can add to them to increase the attractiveness to fish).
If he's actually more interested in predator fishing, it's not so bad, but put your foot down at the prospect of live bait, as it's bloody cruel and banned in most fisheries. And he still might use up his leave to go fishbothering somewhere with nothing for you to do.
And if he's the sort of person who just likes fishing, see if you can go along. As long as you don't expect to talk at all, have no objections to existing on bacon sandwiches and coffee from a thermos and don't scream when he passes you the tub of maggots or casters. And tell him to fuck off if he gets out a keep net as he isn't in a competition and they are cruel/harmful to fish.
It's all catch and release, not killing them and a vegetarian is even more likely to use barbless hooks, be gentle with the disgorger and gentle when they're put back into the water.
I like coarse fishing and I'm a crack shot at maggot pinging with a catapult. I draw the line before maggots in the fridge.