They're hardly undateable, they've all had previous relationships, some long term.
Well, Brent had only ever had a relationship(long term) with his childhood sweetheart. He had never been in a relationship that started with someone who was new to his Tourette's, if you see what I mean.
By the sound of it, Michael's 'relationships' were mostly one or two dates long.
And the girl had not so much as kissed a boy since she had her stroke and here problems with speech etc began.