These Sims cannot have any flirty interactions with other Sims. Instead, they have their own unflirty counterparts, such as:
Crudely Complement Appearance
Blow a Timid Kiss
Ask Completely Inappropriate Question Over and Over Again
Anxiously Confess Attraction
Feebly Ask on Date
Reluctantly Hold Hands
Pathetic Pick-up Line
Attempt Seductive Whisper
Lightly Brush Cheek
Give Half-Hearted Massage
Ineptly Ask for Massage
Reluctantly Profess Undying Love
Reluctantly Look Into Eyes
Nervously Ask to Be Boyfriend/Girlfriend
Whisper Nothing in Particular
Unconvincingly Tease Like a Flirt
Send Unflirty Text
Unflirty Sims will most likely reject awkward hugs.
A Sim who performs an unsuccessful romantic interaction with an unflirty Sim will receive a +2 "Hold Your Horses" embarrassed moodlet, besides the usual +2 "Awkward Encounter" embarrassed moodlet. At the same time, the unflirty Sim will receive a +1 "Flirty Rebuff" embarrassed moodlet.
An unflirty Sim who performs an unsuccessful romantic interaction will receive a +1 "Flirty Disaster" uncomfortable moodlet.
An unflirty Sim who is targeted by an successful romantic interaction will receive a +1 "Moving Too Fast" tense moodlet.