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1.
The point in a new relationship after spending the night a few times where a toothbrush is left over at the significant other's place for use the next morning, hence establishing a beachhead for further invasion. This can either be a good or bad thing depending on the person.
Good: "Hey how is it going with you and that girl you met?" "Pretty good, I established a toothbrush beachhead last week and plan on sending in more supplies next week."

Bad: "Hey how is it going with you and that girl you met?" "Not good, she established a toothbrush beachhead so I had to call in an air strike and ditch it in the trash."
by Anton Vettel October 28, 2010