Narrative:

Being vectored on climb to join J-61 south of ott VOR. Given clearance to go direct ott, which I thought I was doing. However, I was using the #1 needle on the RMI to go direct to ott but it was still set on the ILS runway 36 OM at dca. The #1 navigation radio was set to ott, however I was just too lazy (no excuse) to use my CDI to go direct as I had it set on the outbound radial of J-61. Center asked where we were going, then gave as a turn back towards the route at about the same time I realized my error.

Google
 

Original NASA ASRS Text

Title: B737 CAPT DEVIATED FROM ATC INSTRUCTIONS. VOR, RMI, SWITCHES ARE STILL IN THE ADF POS.

Narrative: BEING VECTORED ON CLB TO JOIN J-61 S OF OTT VOR. GIVEN CLRNC TO GO DIRECT OTT, WHICH I THOUGHT I WAS DOING. HOWEVER, I WAS USING THE #1 NEEDLE ON THE RMI TO GO DIRECT TO OTT BUT IT WAS STILL SET ON THE ILS RWY 36 OM AT DCA. THE #1 NAV RADIO WAS SET TO OTT, HOWEVER I WAS JUST TOO LAZY (NO EXCUSE) TO USE MY CDI TO GO DIRECT AS I HAD IT SET ON THE OUTBOUND RADIAL OF J-61. CTR ASKED WHERE WE WERE GOING, THEN GAVE AS A TURN BACK TOWARDS THE RTE AT ABOUT THE SAME TIME I REALIZED MY ERROR.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.