When you are high/drunk off your ass and walking around like a bum acting retarded or just appear to be blatantly high or drunk. Or both. This term is popular amongst the Northern Virginia/D.C. area. Particularly Burke, VA.
I smoked an L with my homies and walked around campus slaggin so hard.
A derisive term utilizing a Cybertronian explitive "slagging" a rough analog of the "Eff" word,describing hardened dross from the smelting process.
The word slag is also a defamatory descriptor in the UK. Combining the aforementioned and Bayformers a portmanteau of Michael Bay's surname and the Hasbro property Transformers