The most common one I saw when dealing was people staying on hard totals below 17.
Was playing at a $25 blackjack table and this dude comes over and announces to the table that he just lost 800 in 5 minutes in roulette. He buys 500 in green, bets 300 on the first hand. Gets a 15 vs. dealer's 8, pulls out another hundred from a wad in his pocket and says double down. Dealer says to him "you must know something that I don't know". Deals him a 10 for 25. Guy curses under his breath and leaves the table. UN-believable what some people will do with their money.
Sometimes depending on the count and dealer card, I've stayed on hard 15's and 16's all the time. Works well. Supposed "expert" players who are sitting next to me scoff at me depending on what casino I'm at. They can shove it as I color up.