|1.||He's her lobster|
explicative, 1. a phrase used to designate approval of a particular couple's relationship. Lobsters supposedly mate for life.
Also- "She's his lobster"; although, as male lobsters probably ascribe to this rule less often than female lobsters, it is probably more appropriate to think of Ross as being made for Rachel rather than Rachel being made for Ross.
"See, he's her lobster."
- Phoebe, FRIENDS