Someone has just been complaining that they spotted a colleague who is off work sick for the week out and about in their local shopping centre. Apparently if they're well enough to do that, they're well enough to be in work.
One of the reasons a doctor will certify you off work for a week is to give you time to rest and take it easy as you recover from an illness. That doesn't mean you can't leave the house. There's a big difference between getting up at 7am, facing a long commute and a full day at work, and not getting home until 6 or 7 pm; and going for a gentle browse around the local shops/meeting your mum for coffee or some such.
AIBU to wonder why people don't get this, and speak accusingly of anyone who dares to venture outside their front door when they're out of work on a medical cert?