fucking a girl doggystyle and while having your penis inside her ass she takes a shit on your penis leaving it brown like a snickers chocolate and then she gives your shit covered penis a blowjob like if shes snacking on a snickers.
hence snicker snacker.
American: Hey bro, want some chips?
British: So you call these things "chips" instead of crispity crunchy munchie crackerjack snacker nibbler snap crack n pop westpoolchestershireshire queen's jovely jubily delights? Thats rather bit cringe, innit bruv