To stop someone from stealing one of your tater tots. This usually happens when a hungry friend thinks you are distracted and reaches for a tot from your plate. Then you catch them in the act just in time.
Bob: So I told her I don't care what color -- Hey, bro! (looks down at plate and brandishes a fork threateningly) Lay off the tots! I'm going to eat those!
Tom: Dang! I just got tot blocked!
When you are rejected sexual intercourse because of the presence of a toddler
I had to babysit the other day, and that little kid totally tot blocked me.