..had agreed a price of 150-160 baht to go from Central World to Surasak...
Either 150 or 160, already first error by the tourists, not clear on what was at stake.
Second, (but they are excused if here for the first time) no way a waiting TukTuk will bring from CW to Surasak for 150 THB, min would be 200 to 250 - after though negotiation.
Third one, never start debating or escalate.. just leave the tuktuk, give him the 150 and take a taxi; he was pointing finger, many other would have been pointing a knife.