Can anyone call themselves SIR

Only if they've been Knighted.

newtest3

You can call yourself whatever you like or ask people to address you as "yes sir" but it traditionally applies to males only.

But it's not clear if you're asking an English language question or asking about the Order British Empire, which is a different subject entirely, and follows from the knighting of British subjects by the Queen. There are 5 levels of OBE but only the top two (Grand Cross, OBE & Knight/Dame Commander, OBE) confer the titles Sir or Dame.