Villain was extremely loose (50+ VP$IP).

Party Poker 0.50/1 Hold'em (6 max, 5 handed)

Preflop: Hero is BB with , .
1 fold, MP calls, 1 fold, SB completes, Hero checks.

Flop: (3 SB) , , (3 players)
SB checks, Hero bets, MP calls, SB folds.

Turn: (2.50 BB) (2 players)
Hero bets, MP calls.

River: (4.50 BB) (2 players)
Hero bets, MP raises, Hero calls.

Final Pot: 8.50 BB

Results in white below:
Hero has 8s Jc (one pair, jacks).
MP has 5s Kc (high card, king).
Outcome: Hero wins 8.50 BB.

I know it's rare for someone to bluff-raise rivers, but I often call down against unknowns in these situations. If they show me the flush, I make a note of it and don't call down his river raises. At least 10% of the time I catch someone bluff-raising these types of rivers. When I make these calls, I don't make it just because there's a chance he's bluff-raising - I also make these calls for future hands. I want people to know you cannot easily push me over by raising a scare card on the river.