giving away the fact one has a crush by frequently mentioning the crush object in an "innocent" context.
Mentionitis as a warning sign:
"Boyfriend: let's go see Movie X
Girlfriend: Oh, Tony from the office saw that and liked it!
Boyfriend: How about pizza?
Girlfriend: sure, i saw Tony from the office having slice and am now craving one.
Girlfriend: I am leaving you for Tony from the office"