Lulz = I am heartily amused by your comment and/or photograph or other oeuvre. Please allow me to express my amusement tersely.
F1rst = Ahoy gents! I have successfully transmitted my electronic comment before any and all other similar comments. This statement of victory serves as a claim to internet territory, or somesuch.
Gaaaaaaaaaaay = Previous statements or media included above cause me heartache and great vexation. Note- this phrase also implies that either the aforementioned commentor or comment itself prefers homosexual romantic interaction.
Pwned/Pwnage = The adjective and noun forms of "Pwn,"- to express dominance or utter victory. A "pwned" person or object has recently met with overwhelming defeat, not unlike certain Chinamen in certain mountain rail tunnels.
l33t hax0rs = Those capable of extraordinary feats of electric and communication system manipulation. That damnable Whig, Zachary Taylor, is the antonym of l33t hax0r.