A regular customer who always does something like the following (sometimes slight variations). Looks at food options especially the meat items. Baristas observe her handling the meat items close to her face. Picks up the Cheese Toastie at arms length and raises her voice to ask if it has bacon in it. By regular, we mean the person and their routine is so well known by all staff members.  Not an eyesight issue.
Anyhow, she spends about 5 minutes pondering over the bacon and ham options offered (bacon roll, cheese and ham croissant, ham and cheese sandwich, caesar wrap, ham toastie... sometimes even sausage sandwich) verbally whilst at the till. Waits for a queue to build (if there is no queue or a short queue she takes longer). Finally picks. She does no moving, a servant is dispatched to go fetch it for her, 4 metres away.
Then asks for water... Again. She isn't going to pay that price for water, but she has made a staff member go fetch the bottle for her. She declines it as expensive. Prices don't change often, it is exactly the same price as the last 6 months. Spends ages deciding a drink from the digital overhead menus but ends up getting the same one (a latte) that she always gets. 
Finally the transaction completes, Toastie is in... and she has disappeared. She comes back ten minutes after the toastie was done, and after much of the queue has been served. More interesting of all is this person only does this if the person on the till is white.