Step 1: Things required
a headcrab hat (or any headcrab that can fit on your head)
a blood-stained white long sleve shirt
a blood-stained pair of blue jeans
you can get fake blood at any halloween store or you can make it yourself (there are instructables on how to make fake blood).
Step 2: Blood staining
Step 3: Walk like a headcrab zombie
here is a video of headcrab zombies
Step 4: Talk like a headcrab zombie
yabba, my light meh
heres a video of the sounds headcrab zombies make
Step 5: You're all done
now go scare your friends.