A bampin is short for the Dutch "boterham met pindakaas", meaning a peanutbutter sandwich. Boterham is often affectionately called a "bammetje", which is turn is abbreviated to "bam". "Pin" clearly speaks for itself.
Tom- see that guy over there wearing all that stone island clobber, bet he’s bamgin
Bill- proper bamgin, ya know what I’m sayin. That bitch is rich man