Australian slang. Aboriginal origins but now used throughout Queensland and the Northern territory. Can be a verb or adjective. Means PRETEND, used in 3 main contexts.
1. You reckon you've shagged sophie monk ay? you're gammin
2. Damo ripped you off for that q? what a gammin little cunt
3. you lost your phone last night? thats gammin
4. Nah I'm just gammin with you, i can come pick you up