When you have your hair dyed or roots done and the colour runs down onto your head and dyes the skin around it creating an effect similar to the hair on a Lego character.
Dan: Hey Kezza, you coming out tonight?
Kezza: Nah, not tonight, just had my hair done and ive got a Legohead!
The act of strategically placing Lego pieces on the floor in hopes of your partner accidentally stepping on one, and when they cry out in pain, slipping your penis in for a surprise blowjob.
Bro 1: After a nice romantic dinner, my girl was coming upstairs to get freaky, so I left some extra pieces from the Lego Nostromo ship I built on the floor, and when she stepped on one I jumped off the bed and shoved my dick down her throat like a Facehugger in Alien.