Someone who was being stupid, immature ,blunt or retarded.

God he looked like an idiot.

The literal translation of تلم is blunt.
a blunt knife is سكينة تلمة

blunt:
1. Having a dull edge or end; not sharp
4. Lacking in feeling; insensitive
http://www.thefreedictionary.com/blunt

Unfortunately, if we say, "He's so blunt!" native speakers will think that he's straightforward; saying exactly what he thinks without trying to be polite, which is not the intended meaning. تلم is used in colloquial Egyptian Arabic to imply that the person is عديم الحس or لا مبال.

In your context, the said person is so cold, insensitive, indifferent, uncaring, etc.