troche zgaduje; moze chodzi tu o to, ze ktos jest 'mocny w gebie', ze geba mozna psy straszyc, ale nie doroslych;

to tak nudno i poprawnie, bez tego humorystycznego smaczku

Dla mnie znaczenie jest jasne - umowa "na gębę", czyli "gentleman agreement" :) Bez papierów, często bez świadków, oparta na zaufaniu lub zwykłej konieczności. Język jest prostacki i IMO agreement/contract zupełnie nie pasuje, choć znaczenie jest ok.
Pozbyłbym się "gęby", wtedy wychodzi:
"Words won't do, threaten dogs, not adults...", (słowa nie wystarczą) lub:
"Words ain't a deal..." (słowa nie są umową; ain't = don't make, don't mean, wiele innych)

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Note added at 12 hrs (2007-05-01 14:19:30 GMT)
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Jeszcze do głowy mi przyszło, że w drugim przypadku częściej spotykaną formą byłoby coś w rodzaju "words ain't no deal". Koszmarnie niegramatyczne, ale tak potoczne jak oryginał.

You're all gas and gaiters/It's all a lot of hot air. You might frighten the dogs but you don't scare an adult/grown-up person/human being

I think, in fact, that Enzo's suggestion is at least as close as this.

I've read the whole text posted in your other question and I get the feeling that the the recipient of the card has been threatening to do something violent (to him/herself???) and the writer is saying that this is just talk. Especially since the text goes on to say that things are much better and to bemoan the recipient's stubborness.

Going by the full text, it's almost as if the writer had set off to make a new life somewhere and the recipient had first refused to go along with him/her and is now making dire threats as to what will happen if things don't change - but is still refusing to join the writer...???

"... another sense grew up in the twentieth century in which gaiters referred to the senior clergy — such as bishops and archbishops — because of their traditional dress that included those garments, and gas alluded to their supposedly meaningless eloquence. So all gas and gaiters has come to mean mere verbiage."
( From: http://tinyurl.com/2lvyg5 )


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Note added at 17 hrs (2007-05-01 19:14:41 GMT)
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Or:

'It's all just words. You might frighten the dogs but you don't worry a grown adult...'