When Trevor blasted home the opening goal at the weekend, Seb knew exactly what it meant - and he immediately began working out his excuses.
At first he admits: "I said if Trevor scored I would cut my hair, but I will do it in the summer when it is warmer."
Trevor himself only half agrees with the nature of the bet, and, shaking his shaven head, reveals: "Before the game we were just having a kick around and he said to me 'if you score a goal, you can shave my hair.'
"You know you get a grade one? Well, mine is half that, and that is what he is getting.
"If I lost the bet, he was going to be taking my wife out to dinner - and luckily that is not going to be happening.
"When it gets a little bit warmer we will do it, and make sure the West Ham fans get to see it on the last day of the season."
Seb, sensing defeat, relents and says: "Okay, so I will do that for the last game. I don't want to - but it's a deal."
But he is insistent it will be a light trim rather than a military crop.
Trevor, however, is in uncompromising mood, and adds: "He has got some lovely locks and it's a shame they have to go, but now he is going to be an ugly Frenchman!"
Seb's follicularly flamboyant days look like being numbered, however, and Jermain Defoe - no long-haired hippy himself - insists: "Now he has said he is not going to do it, but it is one against all the rest of the lads, so we'll just pin him down."
And Paul Goddard is quite sure that the agreement was "a full shave, definitely not a trim!"
At least the football side of things is looking up, and despite the difference of opinion with Trevor over his next hair style, he admits graciously: "I really enjoy playing with these players. Trevor Sinclair played for two players on Saturday - he played for me as well."